I was thinking the same thing. Musk has done very well on hard engineering problems - now he is entering a special kind of hell running a social media company.
I have no idea why he would willingly take on this kind of distraction at this point.
Why do you assume he'll be running the company? I assumed he would appoint a new CEO and just participate on the board.
If he just wanted to participate on the board he could have stuck with his 10%. It definitely seems like he's looking for a more hands-on role than that.
He just has a different kind of decision power by owning 100% of a private company. But he doesn't need to be involved on day to day operations and can appoint a CEO to do his bidding.