Early childhood development matters a lot, which is why it's no surprise that guys like Hall and Ritz are the best we have. Hall grew up in altitude. Ritz moved to altitude while still a teenager. Both have tiny ankles and low mass. They are not Kenyan, but even in America they were able to grow up in a pretty similar way. In Kenya almost all of the kids are bound to be born in altitude and stay pretty lean. They have a lot in their favor, because in America very few people live at altitude and eating healthy takes purposeful effort.
Still, the USA is a bigger country than Kenya. More people could succeed in running if they care to do so. But why should they care? Running is one of the least lucrative paths to financial success in America and it often means more discipline in lifestyle (as Toni argues) than any other American occupation/lifestyle demands, so what incentive does an American have to excel in running?
The United States has 313 million people and maybe a handful of men and women 10k-marathon runners who can even make a claim to a possible medal at the Olympics. Those top five earn more money than an upper middle class salary, but every other runner who is not them makes less.
Kenya has 43 million people, dozens who have a claim to be a possible medal threat, and even for the second tier of elites it is an upper class salary if they can win any races outside of their country.
Clearly Kenyans have much more reason to care. They can provide a better life by running well. In America winning $50k a year off racing will barely make you middle class. In Kenya you can buy a house, send your kids to private schools, and hire help to watch over your home with that same money.
Whatever you have to say about priorities its clear in America that many successful men and women put work above their family. It's also clear that many class acts keep their family important while still being amazing in their chosen career path. There's just so little reason for any American to pick running as a career option.