I understand both your perspective and the perspective of the maintainers who do it for free. Spending all your time dealing with pull requests, code review thereof, etc is a huge hastle. On the other hand, no one is going to do free work, then pay to have it merged.

I would offer a compromise. Freely accept requested modifications. Project maintainer creates a list of features he/she will willingly merge. Any other contribution would be a pull fee.

Either way, I'm amazed that people working tirelessly for free to promote open source all these years hasn't hit this problem yet (burnout due to lack of proper monetary compensation).

I wish all maintainers luck.