In his defense, he had to ride his horse a loooong way to get to where the action was, and he wanted to keep his cavalry rested so they could make a powerful charge, and so that nice little trot across the battlefield took a while...and the battle was being lost before he got in position (plus, by the time he got to a good vantage point, the charge would've been uphill! better to let the flower of his army get slaughtered than risk that uphill charge!), so he headed home.