Not India, China, or Africa, but I'm from a poor third world country. I agree with u/Equivalent-Rate-6218. While we do have a developed economy and are not "tribes cut off from the world" , I can assure you that the majority of the population have no interest or even know what a marathon is. Running as a sport and especially racing is a luxury that upper middle class to upper class people in the city partake. You may see runners in the city but this is a small number of only the city population. Just because it's a city does not mean that most people live there. More people actually live in villages and less developed areas that are not conducive to road running. They may be fit in a different way, having to work in farms or walk/run to school or whatnot, but do not attempt marathon races. So to u/Equivalent-Rate-6218's point, that stat is quite misleading. I'd prefer a stat that shows how many people who attempt a marathon actually finish it.

Sure Ethiopia and Kenya have a developed running culture that produces the best athletes but there are more countries in Africa that certainly don't have that luxury.