College sports. The NBA and the NFL, two of the most sought-after professional sports in the United States outsource the scouting and training of young talent to college athletics programs. And because the vast majority of professionals are recruited out of college the competition for professional placement continues four years longer than it would if there were no college sports.
The very best athletes play basketball and football in college, but only a tiny percentage of them will make it as professionals. If professionals were recruited out of high school then those that don’t make it would find out four years earlier than they do now. Many of them would look to other sports where they still have chances. Better athletes would go into soccer at earlier ages.
As long as college athletics programs serve as the unofficial farm teams for professional basketball and football, many top athletes won’t have enough incentive to try soccer as a career until it is already too late for them.