It doesn't have anything to do with our "best athletes" playing other sports. It has more to do with the environment they grow up in, and how competitive in soccer it is. I was in Brazil once and watched a group of kids play soccer. They must've been, 10 years old at the most, and they were pulling off set pieces and plays and shit. I imagine playing the game while growing up in America is definitely not as engaging as playing in other countries.