J
Just a guess--the size of the traveling party may have something to do with it. In a normal year, between players, staff, administrators, big boosters, etc., football travels with a very large contingent (huge if you're Clemson, and have roughly one on-field staff member for every player). Basketball maybe a quarter of that or less. The point being, you need lots of accommodations for all the football folks, and tying up hotels and restaurants, etc. a year or more in advance would make sense.
That doesn't explain why SU needs to tie up non-league opponents 5 years in advance. Or why Alabama, Ohio St., etal. 10years ahead.