Comment by AnthonyMouse

I get the feeling it's the combination of Schelling points and surplus. If everyone else is being pro-social, i.e. there is a culture of it, and the people aren't so hard up that they can reasonably afford to do the same, then that's what happens, either by itself (Hofstadter's theory of superrationality) or via anything so much as light social pressure.

But if a significant fraction of the population is barely scraping by then they're not willing to be "good" if it means not making ends meet, and when other people see widespread defection, they start to feel like they're the only one holding up their end of the deal and then the whole thing collapses.

This is why the tendency for people to propose rent-seeking middlemen as a "solution" to the tragedy of the commons is such a diabolical scourge. It extracts the surplus that would allow things to work more efficiently in their absence.