Nebraska will never again reach the heights it had before in the 90's, because it now has lost all the advantages the school had then.
Nebraska was the first school to really get into all the players lifting, and without a doubt many were on steroids. Now every program has an up-to-date weight room, and the players are being tested for illegal substances.
The days of bringing in Prop 48 players are also now gone, and no school profited from the practice more than Nebraska. Throw in an unlimited walk-on program allowed them to keep bringing in players that they did not have to put on scholarship until they proved themselves.
Finally, they are missing the recruiting of the state of Texas, no state close by has the sheer number of quality recruits as Texas, and during their national championship runs, the roster was made up with about 20% of the players from Texas. Few of those kids now even bothering giving Nebraska a second look now, because they never play in the state of Texas, allowing those kids friends and family to come and see them with ease.
Frost is a horrible coach, and totally in over his head, but unless they can bring in the next Saban or someone like that, Nebraska will never again be the power they were.