Despite having a smaller GDP per capita, Ethiopia actually has a smaller but more focused national athletics program that is better managed than that of Kenya.
As for Kalenjin dominating the running scene, it's also partly due to ethnic reasons. Non-Kalenjin are often left out or even sometimes outright discriminated against by the Kalenjin when they try to get into running. Non-Kalenjin such as Marube Moninda report being discriminated against and treated differently from the Kalenjin simply because they're not one of them. The Kalenjin view running as "their" territory.
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Chain migration and domino effects also occur throughout African countries, meaning that if someone goes out and does something successful, the rest of the village or region would all want to follow and do the same thing. In Burkina Faso, there is a single district where all the migrants go to mainly just Italy. And similarly in the Rift Valley Region, when runners bring their cash prizes back home, all of the neighbors want to do the same thing too.
There are also other Nilotic peoples in Kenya that would have great potential for running, but do not have the adequate infrastructure, training, motivation, or even climate to do so. There are a few runners here and there from the NE Pokot region, but since that is the poorest part of Kenya with a very hot climate, the Pokot simply don't have the infrastructural advantages that the Kalenjin have. They are also stereotyped by other Kenyans as violent bandits, poor herders, and cattle rustlers, so the other ethnic groups basically shun them.
In the past, there were actually many runners from the Kisii tribe. Nowadays there are also quite a few Kikuyu and Kamba runners. If you're not familiar with Kenyan names, you probably won't notice if a name is non-Kalenjin, but there are actually plenty of them if you look at race results and rosters. Large races can have anywhere from 10%-30% Kenyans who are non-Kalenjin.
