You need to look at what sports an eight-year-old is playing in the backyard, what sports his Dad is excited about on the TV.
An agile, fast, coordinated kid who's coachable and wants to train hard but is going to grow up to be 5' 8" is not going to make the NFL or the NBA, but if they've got the athleticism to play in the World Cup... well, in the US that kid will be the point guard on the local high school basketball team and also play safety and wide receiver on the football team.
In India, they'd be a cricket star.
I grew up in a European (Holland) country and as boys we'd play soccer all the time, during school on the schoolyard, after school, in the evening and the vast majority of boys in my class joined the local soccer team (me included). Even though we were a local team in a small village, scouts of slightly more important teams would sometimes come to our matches.
Basically, because soccer is so ingrained in our culture, virtually all boys play soccer at some point. That combined with all the clubs that play at different levels, and the scouting network, virtually no talent is missed.
Put differently, when a new Cruyff or Robben is born, there is a high probability that he will be found.
Women's soccer is really a different story. It has only started to take off in recent years and at least as many girls seem to play hockey.
Of course, it should be said that the only sport that really matters is Korfbal/Korfball :).
When we are talking about the really TOP elite of football those kids get into it at age 5. From that age on every day consists of hours of football. There are scouts looking at prepubescent kids all over the world ready to sign them.
In a hypothetical world where every kid plays only soccer, every potentially great soccer player has been practicing the sport from an early age. In a world with 10 competing sports, some potentially great soccer players might have be playing baseball or basketball from a young age up into their late teens.
On the other hand, I can’t imagine the guys that ended up being cornerbacks, wide receivers, safeties, or even halfbacks couldn’t have become soccer professionals given the right culture, training, and desire growing up. Sure, linemen, tight ends, and fullbacks aren’t built for soccer.