Bigger, faster, stronger, quicker, and experience playing against the best teams week in/week out in CFB.
Years ago when I played HS FB, we would always schedule a 4A team for our pre-season scrimmage. We played as 2A but were actually a 1A school. Generally, they beat us pretty good. They exposed every weakness and forced us to play at a higher level. We then went on to generally beat our regular opponents like dogs.
Later around the time Heath Shuler played there, they scheduled 3A teams in the regular season before conference. Very competitive games but my HS lost some of them.... then went on to win big against lower competition.
Playing against the best FORCES you to up your game even when you lose. It shows you what excellence looks like.