They had a pretty active defense up front that year, from what I remember, so it's not like we were going to repeat what happened the year before. Looking at their wikipedia page for their 1996 team, they had 3 LBs and a DT taken in following draft, so that's even more stout than I would have remembered. And being stout and deep up front was really your only prayer for matching up against Nebraska in the 90s.
But beyond clearly having some good talent on their squad, they were another year older and just had great team chemistry, which goes a long way towards an unforeseen improvement (reminds me of Iowa, who came out of nowhere, a few years back).
Lastly, we were simply in disarray that night. It was a horrific game to watch. We had 6 fumbles and 3 safeties. Yes, 3. Friggin. Safeties. .... And IIRC, all of the safeties were self-imposed (a botched option pitch, a snap over Frost's head, and one more that I don't recall).
When you think about how bad our backfield played that night (well, center and backfield), I can only imagine that our line was probably in just as much disarray trying to block that defense that night. Mind you, I don't remember that for a fact, but our team was simply not ready to play that night. It ended up being ok, though, as that 1996 team really responded well, and by the end of the year, they were really playing about as good as anyone in the country. It took several games before that squad really meshed, though.
tl;dr version: Solid talent up front, great team chemistry, and one horrific, almost-unwatchable offensive game from Nebraska.