Nebraska's California connection dried up when Osborne left and they have never been the same. In addition, the Big Ten is a tough gig compared to the Big 8 that they used to share with Oklahoma primarily. Bo was a good coach, but they wanted what Osborne did and they will never be that level of power consistently again. No one is except Alabama in the SEC, Ohio State in the Big Ten has done it through coaching changes, and Clemson in recent years until this year in the ACC. Maybe USC could rise into that again, but I don't see anyone else doing it.
Also, the difference you reference between Alabama and Nebraska is significant - there is no talent base in Nebraska, and the one within two hours in each direction of Alabama is huge. Nebraska, it could be argued, has the smallest talent base in the conference. They are farther from any population base than any other school, and there are few direct flights into Lincoln making outstate recruiting even more challenging, which has been a huge selling point for Fleck to recruits outside Minnesota. Nebraska's "success" is as ancient history to 16 and 17 year-old's as the Gophers.
Also, for Fleck, the West is a great place to be compared to most Power 5 spots. There is a legitimate chance to compete each year with no OSU on our side. And, at Minnesota, people are much more patient than they would ever be at Nebraska.