We're not that good at WR, so benching/cutting him doesn't necessarily make us better. They could use him mostly as a decoy, and throw to him once in a while just to keep the defenses honest. That gets him on the field but also tells him that he's not reliable enough to get more throws. Heck, if he catches the ones he should catch, maybe they increase his targets to let him build a highlight reel.
For the Bills, that's a win-win. Even if he finishes strong, I doubt they'll re-sign him. Someone else will, however, and that makes one less team competing for a receiver who might actually help us.