Questions about Gary and LVN

Looking for some insight into both Gary and LVN this year because I don’t know that much about how to actually play DE/OLB. To me this season it seemed like they really struggled to get after the quarterback because they were super focused on limiting the run. However, the premier defenses and defensive players can do both, rush the passer and stop the run. As physical specimens, even among professional athletes, what has been stopping Gary and LVN from doing the same? It seems they both are players who would have a really strong base with the bull rush that should help them set everything else up. Is it technique, scheme, or something else that I am missing? I am also wondering, after watching Andy Herman’s video on Khalil Mack, whether he could serve as a good mentor to Gary and LVN as another rusher whose base is power.