Combine that with many of our stadiums are full on the same day. Any football Saturday with multiple big teams playing home games, all of their stadiums are full that day. So the Wolverines’ Big House is full on the same day that Bama’s Bryant Denny stadium is full, and the Aggies’ Kyle Field is full, and the Volz’ Neyland Stadium is full, etc (for whichever ones have home games that day). But the whole rest of the world has only enough fandom to fill up only a few 100K stadiums.
The rest of the world build tons of stadiums. There’s 92 soccer teams in England above the “professional” line (though people are still getting paid enough to not need other jobs 2 or 3 more leagues down the pyramid). There’s generally enough stadium capacity in city/town/village for about 20% of the population. English cities are notorious ghost towns if all the local soccer teams are playing at the same time. I’ve joked with a British ex-pat friend that where we have “2 stop light” towns they have “2 soccer team” towns.
And most of the rest of the world follows a similar path to England. Tons of teams, tons of stadiums, very few what we would consider big stadiums, but if you add up the stadium capacity in a city it’s a good chunk of the population.
Most major non-U.S. cities have very large soccer stadiums. And a big cricket match in India will have at TV audience in excess of 1 billion viewers.