Then this is just a chicken and egg situation. If no large reliable organizations had hosted email servers nobody would have used email either.

Not sure I understand. This is exactly the same as Mastodon. You can use an existing sever in which case your account is tied to their sever, or you can set up and host your own.

Why did they do it for email?

But that has nothing to do with the protocol. Google could start a server tomorrow if they wanted

To be fair, the same is true of email

I forgot how good it was