First, and foremost, we easily the luckiest defense in the nation. Every break (defensively) went our way all the way up to the end of the BC game, where the offense utterly melted down into a stinking heap.
Second, Baer's defensive scheme was solely focused on stopping the run. He got away with it because we had NFL draft picks along the defensive line, and also at every starting defensive back position. Once those linemen as well as Walton, Sapp, and Earl left, all we had was Vontez Duff (very good player), and he couldn't carry the defensive team like a full backfield could.
Most of the teams that tried to pass against us that year had a lot of pressure coming after them just from those 4 down linemen, but against USC, which had a very good offensive line, along with a 3 time NFL Pro Bowl QB, 4 NFL WR's, etc. They made absolute mincemeat out of our defense, and badly exposed us for our limitations.