The reason Mastodon and the Fediverse is spread out on so many servers is it protects it from being taken over by anyone. Not even the richest can buy this place.
Centralised services like Twitter are incredibly easy to buy out. If you move from Twitter to another centralised service, sooner or later that will get bought out too.
The point of the Fediverse is to break this buyout cycle, to let people be permanently in control of their accounts. More info here: