Individual season awards are fickle. For example, Rose only won MVP because of public backlash against LeBron. Not that Rose isn't a fine player, but he really isn't an MVP.
Furthermore, often season awards are more favorable towards sudden turn-arounds as opposed to sustained excellence. Besides the backlash against D12, KG and the Celtics have been consistently good defensively for several years. Not that KG doesn't deserve a dozen of DPOYs, but consistent excellence doesn't surprise anyone (and many pundits just waive their hands and call it the system, not the players, anyway).
And, like it or not, Chandler had a HUGE impact.
Last year, the Knicks were 27th in the league defensively. This year, they were 11th. (Going by points allowed).
If you look at opponent FG%, they went from 26th to 10th.
Awards love big turn-arounds like that. Chandler DOES deserve the award. KG deserves it more, but whatcha gonna do?