I used to skeptical, but I could be convinced that there is something to be said for self-publishing.
If you are good at word processing, you can do the typesetting yourself, probably as well as they can if you take the time. Douglas Hofstadter did all his own. It’s fun if you have the right tools. I always liked that kind of stuff.
With enough time and software you can do the figures you need or find them in stock on the internet. Or hire someone to do them — illustrators have a hard time these days and are happy for work.
You can get literate friends to help you edit, though that may be the end of the friendship.
So what’s left? Distribution and PR. And encouragement of course. Are publishers good at that? Their life is a lot tougher in a world where dueling media vie for your attention in multiple ways.