There are plenty of studies that show that people will do things for free that they'll never do for pay, and moreover it's pretty easy to come up with intuitive

There are plenty of studies that show that people will do things for free that they'll never do for pay, and moreover it's pretty easy to come up with intuitive examples of this in real life. Lots of people would be more than willing to help their buddies move, doing many hours of manual labor for free because that's what friends do, with the only tangible reward being pizza and beer at the end of the day. But if your buddy went on Craigslist and offered the monetary equivalent of that pizza and beer to hire movers, nobody would take him on it, as it would be way below minimum wage; if he tried to offer you that money instead of the pizza, you'd be insulted.