Not having a true pass rusher and depth.
We can’t blitz because we can’t trust our secondary to play in space to make the play in the quick game and 1 on 1 coverage.
They also couldn’t gamble too much with the offensive struggles and 2nd/3rd string QB’s.
So they’ve chosen to play 3 DL to play coverage and rally to the ball instead of being consistently exposed.
Is it perfect? No, but with the personnel on D it’s the best choice and for the most part it’s given BYU the best chance to win games.