For a couple of reasons. One, Saleh is on record multiple times as basically saying he wants 8 starting-quality players on the DL. He likes to rotate players to keep them fresh and doesn't want any drop off in level of play and production. Two, while it isn't the only reason the Jets were awful vs the run last season, the play at the DT position beside Q was a major part of the problem. Shepherd isn't the answer, and Rankins was awful vs the run. I could even potentially see them cut Rankins after the draft when they draft an NT.