I wonder if the college stadiums that can hold 100,000 fans do not have all of the luxurious sky boxes and amenities that an NFL stadium has. Perhaps whoever the bigs are in the soccer world prefer the luxury.
That's probably it right there. And you're correct. When I went to Jerry's Field (NFL / Dallas Cowboys) a decade ago to watch a neutral site college season opener between Bama and USC, I was amazed at how much smaller it was (I think 70K compared to Bama's at 100K), but had much better amenities even for the plebes and way more sky boxes for the higher dollar tickets.
I once won a local contest to see a regular season game in a suite with all one can eat and drink served to you by staff and that indeed does spoil you. Nice seats and tvs help as well.