Knox probably realized that this may be the best his numbers would look in his career. You had 5 seniors paving the way for you on the O-line and they will all be gone next year. If he had stayed for next year, you would have seen a contrast like how Le'veon bell looked at Pittsburgh vs how he looked in NY. A good offensive line really makes a difference... Opposing defenses are also learning to shut him down and to take the risk of allowing our QB to beat them... which seems to have worked in the past couple of games.