I think the things about him getting made at Dak was more of an internet fabrication. He may well have wanted more targets, but nothing ever suggested he was the kind of guy to go off on people are make a scene.
My guess is that it was more about his demeanor. Not really a take charge guy or a leader. Sometimes the body language looked bad whether he meant it to or not, and he seemed a bit aloof. Never really saw him on the sideline talking with Dak, coaches or other receivers about what was going on in the game, and he never showed much enthusiasm. The Cowboys may have felt someone making the kind of money he was needed to be more of a leader.