The was a confluence of two items. First, and most relevant to the money discussions, were his injuries: Tommy John and then the thoracic outlet syndrome surgery. His career was changed. But here's the second item. He was either unable to or refused to relearn how to pitch. Add that to attitude ("The Dark Knight hits the town with XXX, supermodel...The Dark Knight hits a restaurant opening the night before a game," etc) and the refusal to go down to the minors to work on regaining his effectiveness. (Granted, if he were healthy, no one would care about his social life...many in fact would be jealous.)
He and Boras were aiming for this year to then get the deal you note Jason. The injuries short circuited that...but he frankly did not endear himself to either his teammates or management with his attitude. Contrast that with CC Sabathia, who went through physical hell a few years ago (including a drinking issue). His teammates were vocally supportive ...and, he remade himself into a finesse pitcher - and an effective one at that.
As a Mets fan since the beginning (1962 at the old Polo Grounds), I feel bad for Matt, but sometimes one compounds the issue by actions or attitude. And...lest we forget, he's a UNCheat guy.