Without federation, switching means migrating both your host and your network of participants simultaneously. That is a much harder and more expensive coordination problem.
Without federation, switching means migrating both your host and your network of participants simultaneously. That is a much harder and more expensive coordination problem.
The switching cost for the average user of a federated system--one which has experienced lock-in on someone else's naming system, such as by using a gmail address or having a mastodon account on a large instance--is brutal. There is an advantage here that that is even possible, and there is then competition between these inter-compatible providers, but there are still many reasons why users tend to end up wanting to end up attached to larger namespaces (all of technical, political, and economical). Hell: even some of the smartest people I know seem to have an @gmail.com address (or worse: have let their identities become owned by a company they happen to work for) no matter how immediately "amateur" that makes them look to me :(.
(I gave a short "talk" about this at the Distributed Web Summit a few years ago, but the video they took has an over-an-hour audio sync issue and I haven't taken the time to edit my own copy yet.)
Address lock-in is real but doesn't fully negate the benefits of federation. Even if you don't control your address's domain, you can switch providers without losing the ability to send and receive email. There is extra cost in pointing your bank account to your new address, but it is possible. If your bank communicated to you via a non-federated protocol like WhatsApp, switching would be impossible.