Also a college HC.... these are all spot on. We have had Kenyan/African athletes in our program at points, so I speak from a bit of experience.
Another reason that has been mentioned but not connected to the main point is that it's not like 100% of the Kenyans in the NCAA system pan out and become NCAA qualifiers. Posts have mentioned athletes lying (true), or coming in out of shape, performances are hard to verify, and sometimes the training they are doing to achieve a solid mark is unsustainable (training camps are hit or miss in Kenya).
So if I have 4 full scholarships at my D1 program (and I do), I might need to spend all 4 on four Kenyans and maybe 1 of them wins our conference and maybe goes beyond, and maybe one other is good and contributes at the conference level too, but it's very possible that at any time the other two may not be good enough to help us win, for any number of these reasons mentioned.
So how does that help me win? I get ~2 high level Kenyans on 4 FTEs or I get 10-15 domestic kids from a variety of levels and backgrounds on 4 FTEs.
Now if you're talking about fully funded programs, I think the jist is exactly what 49er said, you have to be these athletes parents. It's very rewarding to see them grow, but exhausting and takes a toll on you beyond what a job should require. So these coaches have to have a great recruiting network, go to Africa, watch time trials, talk to people, vet athletes heavily, then get them money to fly out and pay taxes, and hope they are eligible and clear the EC when it's all said and done. That's a huge investment on top of a full ride for no guarantee they will ever pay out.