He had a sensational debut game, but as far as I can recall, nothing after that. Plus he's a liability from a fitness and discipline pov. Then there's the question of team combination too. They've got David Hussey, McCullum, Ponting, Gayle, Gul and Mendis in their overseas pool. Mendis has become a phenomenon since the last IPL and there's no way they'll not play him every game this season, subject to availability. Their bowling attack will most likely comprise Ishant, Gul, Agarkar, Dhinda and Mendis if they play 5 bowlers. But that lengthens the tail, so they're more likely to play 4 bowlers at the maximum. Shoaib appears the weakest link.
There's also the consideration that the franchise owner Shah Rukh Khan is just an actor, and is much poorer compared to the conglomerates that own the other teams. He's got to cut corners by avoiding paying people for warming a bench.