That is not even remotely true for the vast majority of sports, @hebegebe . I have never attended a college fencing/tennis/squash/polo/etc etc match but I’d bet money there are very few spectators there.
I live near a D3 college and let me tell you even the stands for football and LAX are basically empty but for a group of parents who live close enough to come and a handful of friends of the athletes. And those are the BIG sports at this school.
OTOH, I have been to totally sold-out music and theatrical performances. Had to buy tickets early or we wouldn’t have been able to go.