I remember when Google Chat added XMPP support. I already ran my own server but some of my friends we're happy enough to use Google. And that was good for a while, but at some point Google had enough people running its own chat that it could simply shut off external XMPP traffic. That was a sad time, because we could have had a federated decentralized chat protocol that dominated the internet, much like email does for its particular purpose, and instead we got fragmented chaos.

The same thing could happen with the fediverse in various ways. So hey, if some commercial entity wants to run their own server, that's cool, but we need to keep reminding our friends of the dangers of relying on that commercial entity.