but people who followed you before will have to now follow you again in the new location, it does not automatically transfer

It's possible to leave a redirect information on the old profile. Normally all your followers are informed about this and automatically follow the new account.

Anyway: this means that you depend on your old profile and server to work at that moment. If the server completely vanishes or if you're banned by the admin for whatever reason you can't set that redirect information.

By the way it's worthwhile to consider that in the case of Bluesky at least right now the whole portability of profiles is depending on some kind of centralized Meta server in the background that manages the identities. Bluesky claims that this won't be necessary in the future, but right now it does afaik still work like this.