3 ideas
Kenyan training camps run most sessions as large group runs that start very slowly and accelerate steadily, often ending near race effort. Runners hold on as long as they can and drop off when they can't. This produces hard efforts without any formal interval structure and sorts athletes by fitness each day.
The Kenyan system pairs very hard sessions (fartlek, hill work, track intervals, tempo runs) with recovery runs so slow they look like jogging, plus a lot of sleep and rest between sessions. The claim is that the extreme contrast drives adaptation. A moderate effort every day does not.
An outsider sees a stream of world-class Kenyan runners and assumes some special method is producing them. A closer look shows a huge base of runners training under tough conditions, where many break down or quit, and the survivors become the visible elite. The result reflects selection at scale as much as the design of the workouts.