Hi, I'm fairly new to these forums myself - I admit, I've lurked here for awhile - but this issue of "too many projects" is very much on my own mind. I come from a writer's background, decided to make games based on what I've written. Writers are constantly dealing with "too many projects", and I remember writing several stories at once, or worldbuilding in several different worlds, or a mixture of the two.
I still do some of that, but not a lot. I've been disabled for about a decade now, so game design is something I'm working at when I can, hoping someday to get a game done and "out" somewhere. But yeah, I occasionally work in little bits at other projects while dealing with the main one I have going right now.
I agree with those who say, "choose a focus and stick with it - don't veer off." Like I said, I have ONE main game project I'm working on; sure there's a couple I add ideas to every so often, or do a tiny bit of worldbuilding for them here and there, but I've learned pretty fast that I can't do like I did with story writing and work on two or three games at once!
I'd say make a physical LIST of the different projects you'd like to do, and keep that as a file. Then, if you want and can do things this way, add little bits to whichever one you want every so often, but have ONE MAIN PROJECT that you keep working at steadily.
I'll also add that in the writing industry there's a common idea of "killing babies", where you actively go about in your files every so often, or in your stories, and get rid of something that is not working. It doesn't matter how much you might love this cute green dragon who is hanging out in the gardens, the question is, how useful is he to the plot? Do you really need to have a three-page interaction with him? Is this conversation going to affect the main character's life somehow? If not, get rid of him... If you look at your projects this way, maybe you can better organize them, by considering seriously which ones might actually work and which ones just wouldn't be worth your time.