...when Utah has been successful, it's been because they have serious depth along the DL and can liberally substitute to keep guys fresh and bringing pressure. Not to say they don't use some blitzing too - but primarily the pressure comes from the front 4 with some well timed blitzes.
BYU doesn't have the depth right now. Too many guys injured, too many guys new. I think you give them another year or two to continue developing players and increasing depth and we'll see improvement over time. But this isn't an easy fix - since BYU was running with 3 DL under Bronco and will need time to develop depth.