All major professional sports teams are managed monopolies. The NCAA is, as well.
There is no other reasonable route for professional football or basketball players in this country. Short of asking people to leave the country to play elsewhere.
Nothing wrong with going overseas to play professionally. And still, there are semi-pro leagues in nearly every major sport. I can think of at least two semi-pro football leagues on top of the Arena League where guys who aren't good enough for the NFL go. This girl I work with is from Little Rock, AR and used to be a dancer for the Arkansas Rhinos of the NAFL.