Why has the exchange endured?
So perhaps the exxchange came, not from an economic drive to allocate resources effectively, but from a framework of justice. The next question I am interested in is why it has endured for so long. One of the potential answers is very simple: the framework of justice has persisted in social relevance. But it is also worth considering other contexts, such as its economic relevance once it is introduced, the legal and taxation systems that it forms a part of, and the discourses that it is embedded in.
Economic factors
Even if the exchange originated from a framework of justice, once it started being used the economic utility may have become apparent and led to it being more widely adopted. I've discussed some of the problems with its economic utility already, and in the next section of this work I'll be engaging more closely with one of its alternatives, non-reciprocal gifting, but here it might be worth considering what historical contexts might have rendered it useful. That is, even if I disagree that the exchange is the best way to approach the economy today, there might be reasons that it was more useful to have the exchange in various periods of history. If most early economies were smoe sort of traditional gifting economy, it would be worth considering the factors that made gifting less attractive from an economic perspective, and made exchanges more attractive.
Classical economists often consider the individual, their ability to rational pursue their own self-interest, and their trust in the system around them, as the main factors to consider in terms of an economic system's functionality. The classical view of the economic individual is that they have little trust and prioritise improving their own conditions.
With these considerations in mind, there are three factors that might explain why the activity of gifting became less preferred and the exchange became more preferred, all of which relate to the trust and self-interest: the level of abundance in society, the type of personal relationships, and the diffusion of reciprocity.
Abundance
The level of abundance could affect the level of trust that an individual has that they will receive enough resource to survive and thrive. If resources are widely available, an individual can trust that if they give away some of their resources, they are still likely to be able to receive resources they need when they need them. If resources are scarce, then an individual might become protective of the resources that they own and be less likely to give them onwards. Instead, they could be motivated to exchange resources so that they are less likely to be in the precarious position of having too little or none.
There have been times of great abundance and times of great scarcity throughout history; but it is not the case that abundance was necessarily correlated with greater gifting and scarcity with greater exchanging. In fact, it is in times of disaster, strife, downturn and poverty that we often see the most gifting occurring, whether this is from community work and provision or government intervention. Overall, poorer people are more likely to gift significant portions of their resources to others than rich people (though there are obviously exceptions). So while the reasoning of trust and protection of resources could lead to the conclusion that abundance is good for gifting and scarcity is good for exchanges, it is often the opposite that occurs and scarcity perhaps instils a sense of empathy and care for others.
Personal relationships
The quality of personal relationships is also a potentially relevant factor. Where communities are small, each person might know or know of the others, making their connection a more personal one. The idea of "self-interest" could extend the idea of "self" to close members of the community - looking after children, siblings, cousins, friends, and so on. In a relationship such as this, an individual might consider providing resources to someone they have a close personal relationship with and not ask for anything in return, the same way that they would provide resources to themselves and not ask for anything in return.
As the community grows in size many of these relationships will be less personal and more anonymous, meaning that more and more people will fall outside the sense of "self" and become "others", with an increased sense of distrust and a lower likelihood of gifting over exchanging. The human population and the size of communities has grown rapidly and radically over time, so if this premise is true then the motivations for moving from gifting to the exchange make clear sense.
On the other hand, there is a sense in which gifting still occurs on large-scale, institutional and international levels, such as welfare, charity and aid both domestically and internationally. And there are occasions of families fighting over resources rather than banding together, including cases where parents send a bill to their child for the cost of raising them (unenforceable, but still indicative). The reasoning here is, at best, a little ambiguous, and I think it indicates that there is something more significant that often affects the behaviour of people.
Diffusion of reciprocity and specialisation
A final factor to consider regarding economic utility and motivation is the scale of diffusion of reciprocity. Both exchange and gift economies have diffuse reciprocity, or generalised exchange, where people contribute to the community or economy and receive back, though not necessarily directly from the sources that they contributed to. For example, a person who volunteers as a nurse might provide healthcare to someone who drives trucks that transport the food that the volunteer nurse eats, so even though the reciprocity isn't direct, it still exists. Similarly, the money that a person pays for their food can be used by the shopkeeper to pay their rent which is used by the landlord to buy shoes from the consumer of the food, once again producing an indirect reciprocity.
Where communities are small and economies are simple, this type of indirect reciprocity is unlikely to be very diffused - a person could see how their contributions assist the community in satisfying their own needs. But the larger the community gets, and the more steps are involved in any particular type of specialisation, the more indirect reciprocity becomes diffused, so that the contributions one makes and receives can seem entirely disconnected. At that point, trust that a person will receive back for their contributions is lessened, and direct exchanges, and the holding of some medium of exchange that allows them to get what they want when they want, might start to seem more viable.
All three of these factors - abundance, personal relationships and diffuse reciprocity - are suggestive that the larger the population gets, the less viable gifting is and the more viable exchanges are. That would pose a challenge for a model that wants to do away with the exchange, but I think the evidence is a little mixed, and there may be some more signficant factors to evaluate.
Legal systems and taxation
One of these is the legal system and taxation. This is an argument that the political structure is more significant in determining the economic structure than the population size or material conditions. Legal force can be based on social norms, rational engagement with arguments about legitimacy, and violence, all of which can be as powerful as material conditions in motivating human behaviour.
The first and most obvious idea is that if the exchange came from the legal framework of justice that was implemented, it would persist for as long as that framework is implemented. If the reasoning behind that framework has been working in society, or if it has become deeply entrenched, then there is no real reason why such a system would not continue indefinitely, continually reinforcing the relevance of the exchange.
Another idea is that taxation could reinforce the notion of the exchange. Governments, traditionally, have needed to raise revenue through things like taxes and tarrifs in order to operate. In order to tax systematically, the government needs to define a unit of account so that they can take the appropriate amount. For example, if the government wants to tax 10% of each person's wealth (however they want to define it), they'll need some way to measure the overall wealth and then calculate the 10%. This starts to entrench the idea that everything has a quantifiable value, which facilitates any exchanges that occur.
Moreoever, a person might need to trade in order to pay their tax. For example, if a person has six cows, then 10% of six cows is about one tenth of a cow - something that the person cannot pay without chopping up the cow. An alternative they have is to trade the cow for something more divisble (for example, pounds of grain), and then pay their portion of the tax with that. Having a clear unit of account would also facilitate that trade - if the unit of account is something usable (like pounds of grain), they might prefer to trade it specifically into that commodity.
Governments have traditionally been very happy to tax in some form or another, which would continually motivate the need for individuals to trade between themselves to place themselves into a position where they can pay the correct amount of tax. The enduring presence of governments - through violence, through consent of the governed, through convention - would then explain the enduring presence of the exchange, with traditional gifting economies functioning in communities and spaces where government taxation is less present or relevant.
Finally, formal exchanges require property protection and contract law definition and arbitration. Once these are encoded, the expectations of the community might be set - these form the baseline that, in the absence of any other type of agreement, form the foundation of economic interactions. There is also a type of "path dependency" that could be present here - that is, the state has invested a sufficient amount in defining these laws and their enforcement that moving away from the system invokes a cost, both fiscal and social. The system is sympathetic to moderate amendment, but not radical change.
Discourse
Another reason for the persistence of the exchange could be discourse. By "discourse" I don't mean a general conversation, but rather something a little more particular and technical, associated with a movement called post-structuralism.
A discourse is a way of thinking and speaking about the world that shapes what someone believes is possible and what they believe is justified. One way this can happen is that the discourse suggests that something is normal, natural and moral, and that other things are not normal, natural or moral. For example, a discourse on gender might say that men and women are normal and natural, and that anything else is abnormal and unnatural - and might even be immoral or harmful to pursue. It might suggest this by framing a non-binary gender as "impossible", and therefore some sort of deceit by anyone who claims that this describes their gender. The discourse defines the categories of the possible and the justified, and then labels anything else as either impossible or a transgression.
In addition, post-structuralists typically suggest that discourses are created and maintained by people in power, and that they do so because it also forms their power. If they can convince people that only certain things are possible and justified, they can use that to control what people can and can't do - and whether people can challenge their power. People can be convinced of discourses without knowing that they have been taught to believe something, and with no idea that they believe a particular way of doing things.
The discourse constructing the exchange is something like the following: the exchange is the natural, moral and normal way of transferring resources, and everything else is problematic in some manner. The exchange is natural because it is embedded in human nature to not give something away for nothing. The exchange is moral because reciprocation of equal value is considered fair and anything else is considered exploitation. The exchange is considered normal because it has been around for so long. Other ways of doing things are looked down on: receiving charity has a stigma, welfare makes and keeps people lazy, and even volunteering is sometimes depicted as a waste of time and effort. And who benefits from framing the discourse this way? Well, wealthy people. The beneficiaries of people believing this particular discourse are those people with things that can be exchanged, such as money and assets. These people have enough money that they don't have to work, and many of them don't, but they are often considered to have "earnt it" or, at the very least, that their parents put in the hard work to earn it and we should not disrespect that work. And the people who receive welfare are often depicted as morally dubious people who leech off the system, or who are placed into a socio-economic trap because their motivations are stripped from them by government generosity.
And yet, if we think about the wealth of someone like Elon Musk, most of it is imaginary. That is, he may have cars and houses and so forth, but that is not the bulk of his wealth. The bulk is shares and savings and financial instruments - things that only exist because we all collectively agree to imagine a system in which they have power. Musk can buy Twitter and make himself be listed as founder of Tesla and run the Department of Government Efficiency not because he presumably has several houses and a private jet, but because he has these tokens which we grant power through collective agreement. That is the power of a discourse: people in power keep themselves in power by convincing others what is possible and justifiable. It is possible to trade shares for tangible goods. It is justifiable to buy things of obscene luxury if you have enough money. It is impossible to get houses for the homeless, and we cannot justify helping the impoverished because of the Budget, because of the exchange.
One reason that the exchange may have endured, then, is that it placed people in a position of power that only exists as long as the exchange is justified by our collective imagination, and so they have used their resources, in part, to keep that discourse going.