The Nebraska DL were beasts against the run last season, but the same guys could rarely make a QB in the pocket break a sweat. That may be an issue.
Do DTs in the NFL normally do that? (I really don't know)
Well they know if the play is a pass play within a second, and often before the ball is even snapped, at which point the DTs are all about getting pressure on the QB. The DEs and blitzing linebackers may log more sacks, but the DTs need penetration to chase the QB, or simply prevent him from planting his feet.
You can always call your rushing play to go away from Ndamukong Suh, but you might have to double team him on a pass play, which creates an opening for the other linemen and any linebacker or DB you might want to blitz.
Last year Nebraska gave mediocre QBs way too much time to plant their feet and watch the routes develop.
I don't remember if Collins was constantly getting double-teamed or just wasn't as effective creating pressure.