That Auburn team was severely depleted with injuries by the time they got to the bowl game. They lost their stud RB and IIRC another good RB who had been the backbone of their Offense. They were not the same team that played the regular season schedule by the time the bowl came around.
And for all these small school cinderellas....its one thing to get up for one big game. Its quite another to play one tough opponent after another week after week. The latter requires depth which they never have. None of them will ever get through a playoff for that reason.
I believe the stud running back didn’t play because he didn’t want to get injured before the NFL draft.
In any case, the Auburn team that UCF faced was a watered down version of the team that beat Alabama.