chicken and the egg situation. Maybe they don't rush much cause they don't feel they have that guy. Or maybe they don't have that guy because they don't rush much.
If the secondary is as talented as the coaches said they were, there is ZERO reason you can't play man with either a single high or split safeties (depending on WR configuration). But even then, it leaves you with 4 guys rushing at minimum. BYU should be rushing 4 every single down, and 5 much more often. Make it so O-lines can't simply double team each rusher and you'd see sack numbers go WAY up.