@tobiaspatton that's not all communities, though. I think bringing a whole university, or a membership organization, onto the fediverse can be really positive and much more comfortable for the members.
For commercial social networks, joining the fediverse gives people a much easier offramp onto network services they control. They don't lose social connections, and soon they'll even be able to move without losing their posted content. Such a better experience than starting over from scratch.