It's a difference in expectation. PayPal tips the balance incredibly far in favor of the person spending money, to the point of royally screwing people who receive money, because far more of the former exist and the latter want to get paid. People don't just want another PayPal, they want something less broken. We could do with some decently balanced payment systems, as well as a few "caveat emptor, all sales final" systems, but all of them have to get traction with the people spending money and those people don't see any problem with PayPal.