College sports are massive and extremely lucrative.
The university I studied abroad at, the University of Kansas, have one of the best college basketball teams in the country and their coach Bill Self at the time was earning $5m-6m a year BEFORE endorsements. That's probably even more now, 7 years later. The university also had it's own 18,000 seater basketball stadium. You would see KU Jayhawk jerseys and merchandise EVERYWHERE ALL OVER. It was a fucking lifestyle for a lot of the non-student fans.
It was insane.
KU's college football team was fucking atrocious and they still had a 55,000 seater stadium. Imagine the University of Lincoln having a 55,000 seater football stadium just for their uni team.
So the best players win the most games and titles and earn the universities the most money. The whole "college sports" experience is also a massive draw for applicants. People want to go to universities with excellent sports teams so they can take part in the fandom.
I'm sure other american users can expand a bit more.