Fediverse

This is more focussed on Mastodon, but we see the same dynamic emerge here with lemmy.world and a few others as well.

I think an important point to note is that general purpose instances tend to invite a lot more free-loaders that have no qualms to jump to another place instead of supporting their own community should the need arise. This makes the "donation funded" model for instances much harder to maintain and indeed (as mentioned in the linked text) raises the likelihood of a general purpose instance selling out to someone who thinks they can monetize the users somehow.