There are some very concrete reasons why Nebraska will probably never return to national contender status.

But, otherwise, you're just talking about teams who have risen to and retreated from their peaks in a cyclical fashion. If that kills a "mystique" than there's really no such thing as mystique because literally every program in history has gone through that cycle.

You'd be a fool to say Alabama has no mystique today. Yet they were every bit as mediocre just about 15 years ago as Florida State or Miami are today. It just meant they were in a down cycle. All the pieces were still there to dominate once they cycled back to their peak again.