Maybe other people aren't. Maybe they want a more graphical interface.
And, I have no idea, but can you use Github Pages with a private repo? Again, I don't know, but if you can't, this doesn't publish the source publicly.
Isn't your source already public if all you do is host static pages?
Maybe. But you can't make directories that you don't talk about on a public repo, because anyone could go and look at those.