I don't pretend to know what went wrong in PHI, but I will give it a shot.
If I had to guess, it is a combination of them drafting a high round QB, then Hurts getting snaps in every game after the first, increasingly nudging Wentz to the sidelines, then him getting the hook and blame for an offense with no weapons, no OL and abysmal play.
I think he is a guy that thought after playing well and putting his body on the line repeatedly, that after signing the extension, he was Philly's guy. Then they draft a guy and even early on in the season start getting him real time snaps. I assume that that means he is taking 1st team reps in practice. When that happens, the writing is on the wall. Then when everything falls apart, the blame was foist upon him.
Not saying he is right, but I get that he feels a bit burned by Roseman and Philly.