Have to say I saw the writing on the wall back in the late 70s when the retention rate was awful - problem was that all the good guys were leaving and all the bad guys were getting promoted. Problem seems to be repeated today - quite possibly because all the dross that got promoted in the late 70s reached the top of the pile and, in turn, promoted people in their own image.
So how do you change it - certainly not by leaving. It probably takes more balls to stay and work on the problem than to leave it but how many people can do that?