I would guess it's a combination of intentional leaks and reporters smelling blood in the water. Maybe also the upper management did something to lose the favor

I would guess it's a combination of intentional leaks and reporters smelling blood in the water. Maybe also the upper management did something to lose the favor of people that would normally protect them from these kind of events (big investors). Or at least put a stop to them. Something to note is that half (3/6) of Uber's board members are internal (Uber employees). So perhaps Kalanick is under no pressure of being ousted (maybe he has tie-breaking/veto privilege as the chairman) by the board, and so people that do want him removed are resorting to leaking bad press, in the hope that external pressure will force a change.