It’s the timing. That schedule was backloaded, as though Oregon was ranked at the time they’d finish 4-8. Only two teams in those first 7 games would finish with a winning record. That allowed a pretty pedestrian Nebraska team, which wasn’t really much better than the year before, to start 7-0 and therefore become a Top 10.
Ohio St this year being game number 5 changes all of that. To ever get into the Top 6 Nebraska either has to win that game or go on a massive run after that game. A 10-2 regular season, depending on when the losses occur, could never have seen a Top 6 ranking.