Kenyan runners have slowed on track down to out of comp testing. Ethiopians are now ahead of them on 5-10km as they have limited out of competition testing. Road testing is poor out of competition hence the recent change on doping for road races.
That's one of the theories. It will interest me if you can get beyond these hypotheses, or rule out other equally supported theories.
It's a hypothesis supported by the facts stated. There are no equally supported theories outside your imagination, obfuscation, and manipulation of statistics.