And if anything, the colleges were the original sports leagues. The Ivy League was a sports league. Football was a sport done by daring-do young men at Yale and Harvard.
The professionalization of sports is a short history. And college sports becoming the huge media sensation it is today also a recent phenomenon.
Also, Baseball being the outlier to Football/Basketball when it comes to collegiate leagues probably comes from its very early professionalization relative to the latter two.
The minor league farm system in baseball was pioneered by Branch Rickey when he was with the Cardinals, and further expanded when he moved to the Dodgers. Everyone else hated it, and MLB tried to stop him multiple times. But eventually the Yankees adopted it too and then there was no stopping it.
Could a single team in other sports go against all the rest in modern times? I highly doubt it.
PS - Rickey was passionate about collegiate sports and the role they played on campuses.
The professionalization of sports is a short history. And college sports becoming the huge media sensation it is today also a recent phenomenon.
Also, Baseball being the outlier to Football/Basketball when it comes to collegiate leagues probably comes from its very early professionalization relative to the latter two.