Let’s not kid ourselves, probably no one is going to make a living from github sponsors, and projects that bring in any significant money are probably written by developers who already make good money do something else anyway. This would basically be beer money to them.
You would be amazed at how people that do not contribute any sort of money to an open source software project will come in and make demands to the creator to implement some feature or fix some bug. Now imagine if they donate $10 and suddenly feel like there is a debt the creator must pay to them by doing what they want.
I will not be using github sponsors for my open source projects. Instead I will continue to ask for things like tickets to conferences or speaking engagements where I can better develop my brand and clout. That’s the way it should be, but that’s just my opinion.