Scott Frost has never felt like a good fit at UNL to me. Had Nebraska never left the Big 12 I'd say he was a great fit there, but his system is more fit for Texas Tech or Arizona than at a Big Ten West school.
I don't buy the system/conference fit theory. There's no reason that a system like Frost's couldn't be effective at Nebraska or in the Big 10 West. It's not like it's a division full of world-beaters, it's been one of the weakest divisions in P5 during Frost's tenure.
That said, I think there are three main failings with Frost's tenure at Nebraska.
First, his offensive system is stagnant. Defenses will always catch up when an offense stops evolving.
Second, Frost hasn't altered his scheme for the players he has, he's still running it like he has the players he wants to have. It's like if CMC was still running the offense like we had Lazard and Butler lining up at wide receiver. The skillset of our 2017 team and the skillset of our 2020 were different, so the offensive scheme adjusted accordingly. I think the 2020 version is more of what CMC
wants to do, but in 2017 CMC did what the team
could do.
Third, there have been a ton of recruiting misses and transfers, which at the end of the day is mostly on Frost and his staff. They've had highly rated classes, but either their talent evaluation is off or their player development is lacking.