You mean it is impossible for them to work a regular job after retiring from the NFL? Keep in mind that NFL recruits from College, and (if you ignore the cases of cheating the system) most colleges have academic eligibility requirements. Therefore pretty much all pro football players also have a college degree (except the ones that get drafted before graduating -- I don't know what that statistic is).

Heck, if I could have gotten a couple million dollar head start in life by working on my hobby once a week, I'd take that even if I had to delay a regular career by a few years.