The games would be meaningless. Football is not like basketball in which 5 guys can get lucky and play lights out for 40 minutes. 16 seeds virtually never upset 1 seeds in basketball. You would literally never have an upset in football. No one wants to see Alabama stomp on Idaho State.
Maybe give every conference a chance to earn an automatic bid. For example, give an auto bid for every conference with a team ranked in the top 25.