Kenyans distance men side have fallen into marathon training abyss. Those who are not injured or burned out, run well. As is, their best marathoner has 3000/5000 capability and something close to 3:50 mile PB.
Ethiopia recognizes the need for speed side development and thus trains more intelligently for 5000/10000 success. Less fixated on volume as a panacea, and thus able to push more quality.
Ironically, the Kenyan 1500/3000 runners are more in tune with the requirements.
I’m sure that the Ethiopians run high mileage, and I’m sure that the Kenyans run high quality along with their high mileage. To perform at the highest level you need both.