Of the four major professional team sports, baseball and ice hockey largely depend on the lower professional leagues to develop players; whereas, football and basketball largely use colleges as their development leagues.
The NCAA allows member universities to issue a certain number of scholarships to students based upon athletic ability (as opposed to academic accomplishment or financial needs).
In the top football and basketball schools, these athletic programs generate sufficient revenue that the system is essentially professional except for the fact that the players are unpaid.
It’s an extremely corrupt system, one plagued by exploitation of student-athletes (the majority of which will not get into professional sports), cheating, bribery, and massively perverse incentives, among other things.
Many student-athletes are unable to do anything with their student status, either because they didn’t have the aptitude, didn’t have the interest, didn’t have the time or energy (due to the demands of the sports program), or we’re not given the proper guidance (they are basically kids who are being exploited for their potential). Many of them suffer debilitating injuries or simply fail to become superstars and are subsequently abandoned by the system.
Either way, many if them have been coddled and pampered since their teenage years and never guided to develop their skills or education outside sports while being spoiled with sex, adulation, and gifts. When they don’t become one of the select few to make it to the big leagues, they find themselves in a tough situation. Meanwhile, their universities have milked them for their economic value without having to pay them for their work. (Universities require then to sign away their personality/publicity rights for life so they can continue to profit from films, jerseys, posters, etcetera, using their names and likenesses without ever having to pay them.)
It’s a sad, dirty system.