These are all hunches. I'll add my own: he was initially just posturing about buying it but when he was forced to do it he was motivated by many things (his personal dislike of Twitter's userbase -which was only partly leftist though it was a very vocal and hip even if sometimes unhinged and somewhat puritanical brand of leftism-, what he perceives happened to his daughter, the Saudi interests, his "I'm not owned! I'm not owned!" personality, etc.). Motivated to do what? Well initially it seems to me he wanted to transform it into more of a right-wing Elon cult (and he somewhat succeeded with the right-wing part). But the mass reaction was a destruction of his reputation. Before this he was usually clowned just by leftists but now it's by a good chunk of the general public. My hunch is that he has started to like more and more the idea that he is "sabotaging Twitter from the inside" as revenge for the aforementioned reasons or just "for the lulz" (it seems he likes to think he does grave things for the lulz, maybe it's desperation to fit in or cope). Wether this intentional sabotage is something that crossed his mind from the very start or something he picked up from his fans ("he... he can't be taking these kinds of decisions, right guys? He's a genius! He must be doing it all on purpose! He wants to tank Twitter") it does sound like something that mends his ego a bit and also the only move that could maybe help restore his old PR image of brilliant player, real life Tony Stark.