The problem is economies of scale, as it's easier to pay someone who specializes in that sort of thing to host your things for you than to do it yourself.

Even I, a nerd who otherwise loves the old internet, don't self-host my website but use a provider (Neocities). When you compare learning HTML/CSS to make your own, quirky, beautiful website with spending five seconds making a Facebook/whatnot page, convenience will almost always win.