Regarding the issue of "why don't more orgs start their own Mastodon instances", you have to remember that orgs, unlike individuals, have legal departments whose job is to ask questions like "if we self-host an instance for our employees, are we protected under Safe Harbor laws, or are we culpable for all data on the server? What if a user follows a feed on a remote instance and our server, via local caching, now hosts illegal content like CSAM or, say holocaust-denial material in Germany"
It's nice to pretend that the fediverse is the internet in 1993 and operates under its own laws, but that wasn't true then, and it certainly isn't true now. There's a utopistic streak of rhetoric thinking that because we're posting on a non-commercial platform, we've opted out of "the system". But that's absolutely not true, and furthermore, it's escapist and defeatist. The promise of decentralized networks isn't as a TAZ to escape the system, but as a means to *change* the system, gradually.