7 of the world's 100K+ stadiums are outside the U.S. (Czech, North Korea, India, Malaysia, Mexico, Indonesia, and Australia) and they're all mainly for soccer and cricket.
Meanwhile, 8 of the 100K+ stadiums are in the U.S. and they're specifically for college football (though some double for NFL).
Not saying there isn't money involved in soccer. But when it comes to loving the game enough to actually attend it, 4% of the world's population fill up more 100K+ stadiums to watch American college football than the other 96% of the world attends big soccer games. Then to top that off, many of those college football stadiums are full on the same day (on a Saturday that's a home game for the Wolverines and also home for the Tide and also Penn State and also Ohio State, etc.). Then when you think about how much denser in population many areas are outside the U.S., you'd think it'd be easy breezy to find 100K fans in a small area willing to attend a soccer game. Evidently not.
When The Mexican National Team plays their games here in the US, it’s a guaranteed sellout, regardless of stadium size. They play more of their “home” games in the US than in Mexico.