WADA allocates what would appear to be a disproportionate amount of its resources to one country - Kenya - because it is an identifiable problem. That is the only plausible rationale for the 22% you refer to.
Doping busts are far less frequent in many Western countries, because, regardless of the actual incidence of doping, the business of beating the biopassport through micro-dosing has become an advanced art, with coaching and medical teams able to provide that expertise - sophisticated and costly as it would be. The village pharmacy in Kenya is unlikely to provide that. Since the early 2000's we know that drugs can be masked and typically are. "You have to be dumb or careless to be caught" (Richard Pound, formerly WADA.) I have no more confidence that doping is under control in any Western country than it is in Africa. I doubt that an athlete could succeed now at global championship level without it.
As far as Mexico City in '68 was concerned, it was unsurprising how Ryun performed at altitude, running nearly 5 seconds off his best sea-level time. But when I saw Keino come off relatively poor performances in his prior events, as well as illness, to run a 1500 time at altitude that he never got close to at sea-level then I would have my doubts that this unparalleled feat was stimulant-free. It was miraculous. But miracles are for the religious.