That's a good question, and one I don't have the answer to, but I would say most if not all of those coaches were not put in positions to succeed. It's hard to change the culture of losing when you are restricted in what you can and cannot do. I would also say that all the coaches after Gruden shouldn't have been hired in the first place. Only Turner has had marginal success after leaving the Raiders the rest haven't even been considered for other head coaching jobs, save Kiffin and Callahan at the college levels.
Originally Posted by Da Swami
"You can't Appoint, Hire, or Declare Leadership" ~ Sonny Barger
"Al Davis thought all owners were dilettantes with a new toy. He said to me many times through the years that owners are often the problem with their franchises, that too many of them think they can run things when they cannot, and the teams that succeed are the ones where the owner hires the best people he can and turns the game over to them."