It has been widely reported that friction has grown between McCarthy and Rodgers. Maybe it had reached the breaking point. So management made a value decision: which is easier to get.......a Superstar QB or a good HC? And, with Brady as a model, it's becoming clear that a QB that takes care of his body and continues to have the passion for the game can be productive at 40. So there could be several more years of Rodgers.
And since they hadn't been winning....and were especially stinking up the joint this year....it was not a terribly hard decision to let the HC go.
Of course, who are they going to get that Rodgers will respect? I don't think they can go get a young never-been-HC guy because Rodgers will just roll his eyes at the guy and do what he want to if he doesn't agree with him. It worked for the Rams because Goff was a "failed" 23 year old QB and so he was open to a super young McVay.