The number of tourists in Kenya who from Canada and the United States is low. I have to suggest why it happens.
As a traveler who's tired of long plane flights, my first answer is that Kenya is a loonnngg way from Canada and the U.S. It takes between 17 and 27 hours to fly from Detroit to Nairobi -- and the least cost is between US$3,300 and $5,000, round trip.
Also -- Canadian and American travelers have usually focused on the monuments and cultures of Europe, rather than the wildlife of Africa.