Why not? That's how proper English text is written. Of course there are many programs that can't handle it properly (or handles it inconveniently) so in practice it might be problematic at times, but otherwise I see nothing wrong with it.

Why compare with English? It's computer domain, it's not a book or a poem. It should be clear and unambiguous.

Caps are annoying to type, and difficult to remember (Do You Caps, or Do you caps, or DO YOU CAPS, etc).

Spaces are nuisances that bring no benefit. At best we should use non-breaking space for filenames, but that would be even more atrocious.

Generally just because typing it out with tab completion in zsh sucks, and I don't see a good solution (if it was solved nicely it'd be solved already)