from what he’s said about his experience at twitter it sounds like the company took on a life of it’s own and a lot of the negative things that happened were a product of fiat incentives, and by the time he realized that he didn’t have enough control over the company to change it’s course, so easier to just build something new where the incentives are pure. i’m sure he has many regrets from that period but like mcshane said this is a redemption arc