I think some of this has to do with Joerger's rotations. If we consider Cousins, Gay, Afflalo, & Lawson as our players that are capable of scoring/breaking down a defense, the majority of the minutes when Cousins is off the floor has one or fewer "scorers." 28% of the minutes w/o Cousins on the floor has 0 scorers, 35% of the minutes w/o Cousins on the floor has 1 scorer, 23% of the minutes w/o Cousins on the floor has 2 scorers, and 15% of the minutes w/o Cousins on the floor has 3 scorers. Compare that to when Cousins is on the floor: 3% of Cousins' minutes has him as the lone scorer, 11% of Cousins' minutes has him & an additional scorer, 25% of Cousins' minutes has him & 2 more scorers, and 60% of Cousins' minutes has him & 3 more scorers.
As you can see, when Cousins is on the floor, he's much more likely to have multiple scorers on the floor with him based on Joerger's current rotations. If Joerger was better about balancing the amount of scorers we have on the floor, I'd venture to guess that we wouldn't be seeing such a discrepancy. It will also probably go up once we have a guy like Collison to mix into the rotation.