He wants Freshman to have a chance to get used to workouts and going to class before the football season starts, so that any issues adjusting to college occurs before football season begins. It is one of the reasons you hear of players (particularly Freshman) being required to sit out during fall camp to clear up academic issues. It also allows the Freshman to get to know the rest of the team before the start of fall camp.

Perhaps Bronco changed it but, last I knew, this is his policy for incoming Freshman.