It's not at all clear to me why we allow American football and universities to have such a perverse relationship, when it's plain to see that football itself has nothing to do with education, except insofar as it's an activity that many students enjoy (but there is no shortage of other non-academic activities that many students share, such as baseball...) And in cases like this, where students are leaving the game ea…
College football is just one sport among many popular college sports in the U.S.
It began as a club-type extra curricular activity but as it became more popular universities likely saw it as a way to market their school and attract customers (students).
The top 30-40 programs produce $100 million in revenue which is usually enough to be self-sustaining and help pay for all the other sports teams on campus.
College basketball, baseball, football, track and field, and even hockey in some places are de facto minor leagues. The power and influence of the NFL is probably more to blame for the lack of a proper minor league in football.