I do this for ME. It is an outlet for my creative expression. Sometimes I see work someone is doing, or that I am doing, and I'm inspired how I can make a tool or improve existing software that would assist. Maybe others can benefit from it.
Sometimes folks say they really like my addons but they want certain features and so will "withhold" stars in the rating until they get what they want. Seems kind of like cohersion to me. Not a good idea.
I'm sometimes asked, "Where's the Donate button?" I've chosen not to use one because the layout on AMO* feels to me a bit like soliciting, and it implies funding for continued development, and I'm just not able to promise anything. However, there are some who sincerely want to express their thanks for the benefit they've received from my work. If you wish to make a donation, you can PayPal me at email@example.com.
*(I have seen sites that have a “tip jar”, which I think has a more favorable implication)