Exactly the reason why they might look to trade him. They have holes on their roster and a rotation at the big spot of Ibaka, Biyombo & they drafted Stephen Zimmerman.
Tying up that much of their salary cap (Ibaka + Biyombo + Vucevic) on bigs makes them sacrifice considerably at other positions. For example, they need ball handlers pretty badly.
Vucevic (offense) with Horford (defense) would be a great pairing.