Unfair balance, ie Navy should never beat ND, so when they do it's actually a big deal. Life is not fair, college football reflects life.
Guys playing at Texas named Colt McCoy, or guys playing at LSU named Jean-Fransioux (I have no idea how to spell it)
Generally hospitable people from opposing teams who don't take themselves too seriously vs. NFL people who need to get a life.
Big old stadiums
For me, I also think it happens to be that during the week, I focus on getting to Saturday (the very next day after the work/school week). I know I wouldn't say the same if I was a bigger fan of the NFL, but I personally associate Sundays with "ugh, have to go back to the grind tomorrow."