The NFL doesn't require a college degree - it's just that playing college football is by far the best way to learn how to play professional football and to get noticed by the NFL teams.
Most college players don't go on to be successful in the NFL, but for those who do, college was a very good investment.
College football is a huge institution and money maker. 100k attendees to college football games in the South Eastern US is a norm. It's like a minor league for the NFL. Most of the schools represented are excellent, but not necessarily academically better for general education or undergrad work.... Although being an alum in the region can be helpful in firming work.
Most college players don't go on to be successful in the NFL, but for those who do, college was a very good investment.