Within 2 summers, we saw a strong swing in our class sign ups. Canoes would scarcely get out on the pond, while we filled every kayak class to the max. Kayaking is about balance and even paddling, but only by yourself in the boat. The learning curve is very quick and you can do it all by yourself.
On the other hand, canoes require more paddle skill, muscle, and teamwork. Piloting a heavy aluminum canoe is no easy task, especially for your first time. All this extra effort drove the campers nuts. Of course they were going to prefer the kayaks.