Since August 20th, the betting spread for the game has been alternating between Ohio State -1.5 and Ohio State -3 based on both the bookmaker's feelings on the game, and where current bettors have been placing their money.
Though the aforementioned reasons are "huge" when it comes to pre-game line movement, things like weather, injuries, and rivalries or team history also play into it. Seeing as this is an enormous revenge game for the Longhorns, the line has been moving more than usual for ths matchup.
Depending on the sportsbook, the line may only move once or twice before each game.