I would guess he got caught lying to Donald.
According to the Butler, lying to Donald Trump is not one of the things you don’t ever do.
Maybe not lying, but is sounds like not following the same blueprint. Probably figuring he could persuade Trump that he needed these guys because of experience, etc. I like Christie but he was the head of the Republican Governors Association and is very much an “insider”. Trump may allow him to pursue other opportunities in order to stay true to his own vision and to Drain the Swamp.