Same reason I am highly critical of Jack Dorsey's BlueSky and its attempt at rolling out a separate protocol. The last thing we need is for the Fediverse to be fragmented into a dozen protocols that do things ever-so-slightly differently and prevent network convergence.
Another reason to avoid it is that Jack Dorsey supports known anti-vaxxer and general conspiracy kook Robert F Kennedy Jr. Not the kind of people I'd want to run my social network.
It is very easy to argue that network convergence is NOT a good thing. That's the whole point of the "embrace, extended, destroy" point you responded to.
The point being is that inventing a new protocol is either a case of Not-Invented-Here syndrome or an attempt to fragment the ecosystem - hence jumping straight into the extinguish phase. It does not paint BlueSky as a good actor in this race - especially as there are no substantial improvements over ActivityPub as far as I can tell.