For me at least, the answer is that my side projects are about more than money (though they are about money too!). Developing things myself is the primary goal

For me at least, the answer is that my side projects are about more than money (though they are about money too!). Developing things myself is the primary goal - it’s deeply satisfying to build your own project from the bottom up without having to write specs, argue about design trade offs, do code reviews, etc. The fun is just being able to build without the social overhead. As soon as you have people working for you, that whole equation changes.