I haven't watched Penn State enough to know for sure but the story has been that his OL has been so terrible that it's making it pretty tough on him. And the stats seem to back that up - Penn State was #119 in the country in sacks allowed last year. Twice as many as NU on about a third more attempts.
Nebraska's offensive line has been just as bad if not worse.
The sacks allowed stats are hardly applicable because the two are completely different QB's in different offenses.
Hackenburg is a statue, Tommy is mobile. Where Hackenburg may be sacked, Tommy uses his legs to avoid.
This also affects the way a defense plays you. For QB's like Hackenburg, a defensive line is able to pin their ears back and rush quite a bit more where as facing a mobile threat/dual threat, the defensive line is more apt to play cautious in certain scenarios.
Nebraska and Penn St. may both have horrible offensive lines.
I've watched Nebraska with my own two eyes for a lot of years now and I can say without a doubt the offensive line has not been much help to Tommy's development. Hopefully all of that changes this season.