It is pretty simple really. The Kenyans and Ethiopians race as individuals. It is not in any individual's best interest to push the pace (except perhaps for folks who know beforehand that they have no shot - then there is some possibility that the field will simply let them go).
hard to explain why the kenyans and ethiopians just hand these races to mo - they knew Mo ran 3:28 but they run slowly. anyone have a good answer to why?
You think of the Ethiopians and/or Kenyans as some sort of team. That is the flaw in your thinking. Think of them as completely independent individuals, shooting for their own individual glory, and then what plays out before you time and time again becomes obvious.