Yes — assuming it is safe — I have a family to support and care for (so have to think of them, too).
I want to see what's there — and see it first hand for myself.
Similar reason why I travel to different parts of the world to see things.
I think this is more than just curiosity.
That is what happens on Mastodon now when someone moves their account from one server to another — you get a notification of them following you from the other server.
It depends on what you mean by "replace".
The Fediverse may cause centralized social-media networks to join the Fediverse.
There are some hints of that happening now.
Facebook / Meta has created a new social-media network that is part of the Fediverse.
Tumblr and Flickr are said to be joining the Fediverse.
So, some "popular social media" may become one with the Fediverse.
@hitmyspot
It is all automatic.
You maintain the same relationship after the move.
If you just followed them, but they didn't follow you — that continues after the move.
If they just followed you, but you didn't follow them — that continues after the move.
If you followed each other — that continues after the move.
It is all automatic.
...
As a user, if someone who follows you moves their account, you see that as a new follow in your notifications.