SjmarfBirthplaces of the 100 fastest 10,000m runners of all time
PowerCrazyThe topography explains it all. geology.com/articles/east-africa-rift.shtml
tl;dr The people of that area in East Africa naturally live close to sea level, however there are easily accessible elevations changes that distance runners have trained on for probably centuries. It turns out that training at high altitudes and recovering at low altitudes provides a tangible and demonstrable advantage compared to just single elevation training.
This can't be the whole story, otherwise we'd see places like Chile, Peru, and India competing too
India? the sea and the himalayas are too far apart to compare.
India's Deccan Plateau is about as elevated as most of Kenya's highlands and takes up basically the entire land area of India that sticks out into the ocean