He gets the existing infrastructure, the existing data, the existing userbase which is now forced to provide some type of secondary authentication for identity verification who would probably not otherwise if a new service were launched and probably got many sign ups from people who wanted to keep reading tweets/tweet replies. Not only do the hundreds of millions (billions?) who use Twitter now get shuffled into the system but all the data on them is now at his disposal as well.

Oh and he gets to position himself as a free speech savior while the populace is boiling and ready to backlash at the left and the globalists. Making people putty in his hands