No, the encouragement to use github is github has a good bug tracking system, so if people report bug/suggestions there they won’t get lost.
Some devs have a way to donate.
I can’t claim to know why most devs make free plugins. I do it mostly because it’s fun. But it is nice when you see your modules used in other people’s videos. For me, that’s my “success metric”. If I make something and no one uses it I might (might) decide not to make more things like that. If something is very popular it might steer me to making more things like that.