You are right, something happens, may be in the last 3 years. But is not something as people thinks.
For what I know (really not so much), there are no coaches or managers involved.
It seems there is some doctor and some pharmacist who approached directly some local athlete (not of international level, and in the most part of cases not able to compete abroad), telling them "why you don't use something I can give you, don't worry, it's legal, and you can improve of 1 minute in 10 km. You don't need to pay me anything, but can give me 15% of your price, since you don't have any manager".
In Kenya, at the moment, there are many local races, and of course there is no antidoping. The first prize can be, for example, 50,000 Kenyan Shillings (about 600 USD), with some prize till the 5th position.
There are also a lot of athletes without manager, that need to survive and, winning some local race, to put themselves in evidence for the future.
Among this level of athletes, without any organisation and without real knowledge, doctors and pharmacists "cheaters" had good chances to fish some desperate.
Some of these athletes (many of them thinking to use something legal) became able to go abroad, continuing to take the "support" already used, or with a new manager, or paying their ticket themselves (this is the case of the most part of athletes running in Asian Marathons). In those marathon there is antidoping, and they are positive without knowing why.
I can exclude the hypothesis there is something organised in systemic way. In Kenya, there are big groups of athletes training together, many without managers, and many with different managers. So, no central organisation, and managers and european coaches don't have any control on the group.
If we want to find some info, we need to go "inside" every group, because can be only inside groups already contaminated that the phenomen goes on.
AK has a very hard work to do, because in Kenya there isn't a law (like in Italy and France) making criminally guilty doctors and generally people pushing this type of drugs.
For what I know, AK takes this problem very seriously. The Federation asked to be helped by IAAF and WADA for having blood tests, because doesn't want to hide the problem.
Also, there is the plan to give more infos to athletes, in the most part not educated, about the rules and the position of some medicine (doping or not), because the most part don't know what is legal and what is not.
In my opinion, not more than 10% of the "positives" are really cheaters, 90% did some mistake for ignorance and/or because themselves cheated by the doctors / pharmacists I spoke before.
A correct education can avoid, for example, the possibility to use traditional medicines, coming from trees and flowers, because nobody knows what there is inside.
Exceptions can exist, for example Mathew Kisorio. But I can be 99% sure that nobody of the top athletes is in this group, because they don't believe EPO can work, they have more specific education and can ask to top managements, and they are already the best in the World being clean, so there is no reason to try something else with the risk to be caught positive.