Wow.
I bet you think you brilliantly discovered the problem!
Run all you need to! Be like the Kenyans! Yes! American laziness is the issue.
Reality:
Your blanket assumptions are so fraught with fallacies that the untruths, themselves, can run a marathon in Nairobi.
Why?
Lineage.
Kenyans are of Kenyan lineage, most of whom have a link to a common bloodline. As a result, the fast/slow twitch ratio is different from others but common to Kenyans. Look at the body structure of the typical Kenyan and it is decidedly ectomorphic. Your typical Latino American, Euro American or Arab American is not typically built like that.
As a result of the ancestry, lung capacity is different. Yes, in many ways lung capacity is genetic. We are not all born with the same lung capacity no matter how loud we can scream or how deeply we can breathe in or out.
This leads to the environment. Unless they are living right in the city of Nairobi, the air is generally cleaner in Kenya. This means that the air is lighter which makes running easier for breathing.
This is why some of our athletes go up to Mammoth Lakes,.CA for training.
Why mammoth lakes?
Because until you can tell me that a 2:04:58 on a day when the Kenyan winner got a time only 1:56 faster than that, or just over 4 seconds per mile faster, is a bad time, I am surely convinced that our Americans are doing just fine.