I think it's about their top 3 WR...

... more than Reynolds himself. That trio is so good- anywhere on the field and in any situation- that they're just not going to sub him in. Then with Gurley and, as we've seen, Higbee in there as a blocker they're in 11 personnel virtually all the time. I agree and think Reynolds as a red zone regular could work. But I also understand why, for now, he's a pure injury replacement.