The assistant coaches leave because successful programs get raided. The Packers are losing people, too. Somewhere, folks get the idea that because they worked at a place where winning happened it will follow along with the underlings. Often it does. 

The players leave early to chase the money-again, it usually only happens with a winning program so the player gets noticed.

I have no knowledge of the Asst. AD problem. IMO, I wouldn't be one bit surprised if Alvarez is not a complete angel.