This is a situation I'm fairly well acquainted with since it is not dissimilar to open source software projects -- which is something I have been doing for more than 20 years :-)
It is clear to everyone that people's priorities change over time and that while you may have put a lot of time into leading a project in the past, nobody can expect that you continue to do that indefinitely unless you are paid for it: Life often just intervenes, you may have a new job, a new family, kids, etc.
A question to answer for you is whether you actually care about the project's long-term future. If you were the only one who ran the project, then walking away from it will simply ensure that it is dead. If you think that there is little loss in this, then so be it: It's your project, you're free to do with whatever you please. But you may actually have feelings for it that go beyond it just being a "job". Indeed, I read from your description that it has actually led to a lot of good, and it sounds to me like you think it would be a shame to just close it down. In that case, you'd have to find a way to hand it off to someone else.
Now, good leadership often includes mentoring people to take over from you. Among my proudest achievements as a founder of two open source software projects is that I feel that I could walk away from these projects and very little would actually change: There are people who I have passed all my information on to and who can (and frequently do) fill all of the roles I have in these communities. If you care about the project, and you haven't mentored others who can take over from you, then now would be the time for that: Identify who could replace you (individuals or, better, a whole group of people), have conversations with them about transitioning, and then teach them what all is involved in running the project.
Hopefully you can commit enough time for long enough to bring people into the boat and teach them what they need to know to take over from you. If you manage, the project will survive and your place in its history will be assured.