This, the problem isn't the shots per se, it's the 0 assists.. His job as a PG is based on the different routes run and screens set by his teammates to initiate the creation of a scoring opportunity. even if it isn't a very good one, odds of success are better for Favors/Kanter post up than for a Trey shot...
Some of this still comes down to his lack of physical attributes. Being short and slow makes it hard to get easy passes too. Exum has a much easier time passing the ball just because he is so much taller. Nor does Trey show any particular nice passing skills, maybe average at best for an NBA pg. Yeah, he does make some nice ones, but not many, and makes too many poor ones or just misses opps all together. Yup, he does have hero ball syndrome.