It's step 1) of the scenario outlined in this comment:
Re:Meta preps new social app
by burn_cycle on Monday May 22, 2023 @06:19AM
(#36029471)
It doesn't even have to be this convoluted. They can just do what they did with email. Step one, wait until they have the vast majority of users, then due to spam/'problematic' content, algorithmically block the vast majority of other instances from interacting with theirs.
This can be interesting.