At this point, going back a few years now, there have just been far too many unaccountable, downright weird at times, terrible decisions on the part of Bill Belichick. I won't list them all. You know what they are.
When I see Bill these days, I see a different guy. His methods, at least to the extent that he still has the stamina to stick to them, no longer work; and at his age, it's just not in the cards to change them. (I'm older than Bill: I know the feeling.) What seems like stubborness, or firmness of resolve if you like, is really just desperation, even a sense of being a little lost. You see it in his eyes. You see him unable at times to play quite the angry bear he once did.
I think it's time for Bill to go. When I retired, I knew it was time to go: I think Bill knows as well. I hope it can be managed in a way that honors his past accomplishments, and I'll be an eager participant in celebrations of his accomplishment after the fact, but it must be done.