Jerry has a ton invested in Garrett -- personally and professionally. To just cut Red Pube lose at this point means, by default, that Jerry has wasted 10 years and a lot of money. It makes Jerry look incompetent, which of course he is.
So Jerry may be a victim of the Sunk Cost Fallacy, that a sum paid in the past may somehow influence decisions about the future. The way to salvage some small amount face would be to keep Red Pube on in some kind of front office job, like he got promoted or something.
That would be the worst thing you could do for an incoming coach, and the players. I'd be amazed if any incoming coach even agreed to it.