Because its completely reasonable to assume there are going to be tons of fast people outside of sprinting and American football, which when it comes down to it are pretty niche on a global level.
The reason the NFL has lots of ex-sprinters is 1) it has positions where raw speed translates better than to other sports and 2) its talent is drawn from the US college system, where multi sport athletes are the norm because those colleges have so much money and resources to facilitate it compared to most nations.
I dont know why you're so incapable of accepting that the majority of would be sprinters will never actually pursue sprinting (or American football). A naturally very fast kid somewhere in Africa is almost certainly going to be playing soccer if hes playing any sport. That also applies to Europe, South America, and to a lesser extent parts of Asia and the Caribbean.
Well aware of all that, I do keep up with world wide sprinting, know all about the African situation. A lot of them end up over here at our schools, Hell the fastest sprinter ever at Stanford, Azusa Pacific, Lubbock, Missouri, BYU, were Africans.
But........when it comes to world class sprinting the USA and Jamaica rule. Between the two they have won more Olympic medals than the rest of the world......COMBINED.
Olympic gold medalist, tons of world record holders, tons of world rankers, that is NFL speed, and we see none of that kind of thing in soccer or any other ball sport.
This well if......means nothing.
lane
1,Frankie Fredericks Namibia/BYU
2.Davidson Ezinwa Nigeria/Azusa
3.Chidi Imoh Nigeria/Missouri
4.George Daneils Ghana/Colorado***********
5.Divine Odurudo Nigeria/Texas Tech.....best sprinter
6.Daneil Effiong Nigeria....Lubbock
7.Leonard Myles Mills Ghana/BYU
8.Ododi Nigeria/Stanford
But .....no African has ever won an Olympic gold.
********** fomer decathlon champ Bill Toomey was part of a goodwill tour in Ghana, while there he came across a speedy little kid named George Daneils, beng a Colorado alum..............Daneils ends up at Colorado.