In 2023, Bluesky’s CTO Paul Frazee was asked what would happen if Bluesky ever turned against its users. His answer:
it would look something like this: bluesky has gone evil. there’s a new alternative called freesky that people are rushing to. I’m switching to freesky
That’s the same argument people made about Twitter. “If it goes bad, we’ll just leave.” We know how that played out.
with XMPP there’s the cautionary tale of Google Talk. For the rest I’m not aware of such an example but email is becoming more centralized than ever and RSS is much less prominent than it once was, mostly replaced by profiles to be followed on closed off platforms.