Why did Chris Evans quit?

He had decided on this move a long time ago and had announced it as far back as 2014 (link). Avengers 4 was always going to be his last MCU movie. He didn’t want to become stale in the role–“You want to get off the train before they push you off,“ in his words–and he has wanted for years to do more directing and producing. Being in a huge franchise like Marvel helped launch him into more opportunities, but the schedule didn’t allow him to commit himself to roles behind the camera. This was a long-planned career move on his part and I wish him well.