I remember reading something saying he has a poor work ethic. I can see why you don't want a disgruntled guy with poor work ethic in the lockerroom especially if they don't bring anything on court. This is how you change the culture of a team. A D-leaguer who will fight for minutes at the 4/5 spot and work hard in practice and jump for ever loose ball is worth more than Bargnani. If he's going by Pop's book, this is a classic move. The principles come first. If you have to get worse to get better, so be it.
Story was when he was on the Knicks and PJ was attending a practice at the tale end of Bargnani's last injury, you know the calf strain that lasted 4 months. He saw Bargnani standing on the sidelines while the guys were doing sprints up and down the court, he asked Bargnani why wasn't he working out and Bargnani told him the medical staff advised against it. That pissed PJ off, he tells that story as an example of why the Knicks let him go, lack of effort and motivation. The only guy in the NBA that could break a nail and be out for a month.