When he finally cracked the lineup as a starter in Philly, he almost completely lacked playmakers. It wasn’t enough for him to be a game manager, which I think he could’ve done in the NFL. He had to make things happen. The deck was somewhat stacked against him, and with his size and arm strength, he was always going to have a short leash.
That and he was too competitive for his own good. He’d press sometimes even when the game was out of hand, and he could really go down in flames.
All that said, as has been mentioned, 14 years in the league is exceptional, period.