Kelly Dwyer looks at this question on TrueHoop. One reason - "Lazy Luol Deng"
Lu isn't lazy. He works his tail off, is a right giant off the court, and is a sublime talent between the lines. For the first six games of the season, however, he was a mess offensively. Why's that, top cat? Because the man wasn't putting any effort into the mid-range jump shots he used to dominate with. The knees weren't bending, the follow-through wasn't there, and (not most-importantly, but most-egregiously), and his body wasn't squared. Even on quick-hits, ones that saw him flashing to the front or left side of the rim (Paul Pierce-style) for the short hook, he wasn't jumping high enough and getting his shot swatted. With five gears in reverse, Luol turned into an ordinary mug, and the results weren't pretty.