Why Don't They Make College Sports Manga? Is College Sports Not as Big as Highschool Sports in Japan?

I read a lot of sports manga, and I've noticed that most focuses on Highschool Sports (Baseball, Voleyball, Basketball, etc.). If it's not highschool, it's in a professional setting (e.g. Hajime no Ippo).

From reading baseball manga, I know there's at least a college league for baseball, but why isn't tackled more?