The difference is every girl in Nebraska grows up playing volleyball, over anything else, and the whole country plays football, though decreasingly so, save a few states in the south .
The amount of D1 vball talent produced in Nebraska is remarkable. I remember doing a study of Big Xii rosters in the 90s, and only the state of Texas had more players on rosters in the XII than Nebraska and it was relatively close. 20+ million to 1.5million. On a per capita basis it is Nebraska by a wide margin in the US.