I don't think there is much mystery to this. Reibus said, "It's either him or me," and Trump showed him the door. No one on the planet would take the Chief of Staff position with Scaramucci in place. Why someone with no public relations experience what so ever would have ever gotten the job, is the real mystery.
That's not really a mystery. The guy doing the hiring is an insane, incompetent moron. The Mooch is a natural consequence of Donald Trump.