those kids only have so many college games, they want to be on the field. also, a team like that, the stars are pushing for major awards like the Heisman. They need that last game to be fresh in voters' minds and they need the stats to be competitive.
besides, guys like us are going to be rehashing that game for the next 40 years and I do not want to spend it badmouthing Coach Whatshisname instead of reliving our undefeated season.