I'm not sure I agree that hardly anybody stayed at AKL. I stayed there several times before buying in at AKV, and it was one of my top two favorite resorts. Every time I stayed there it seemed quite busy. On one of my trips when AKL was pretty new, the bellman said they were either totally booked or very close to it. The only downside I think some people feel it has is that it's pretty remote. I've heard that the easiest deluxe resorts to get last minute reservations at are the Yacht Club and the Grand Floridian, though I don't know how true that is.
When we took our DVC tour (which we actually took after buying in), our guide mentioned that of those that tour the SSR and AKV model units, 80% buy at AKV. I know that DVC offering AKV pushed us over the edge into joining DVC. I live the ambience of the resort, plus it's just super cool to wake up to see a giraffe right outside your balcony. I also think AKL has wonderful dining options. I'm really looking forward to Kidani Village opening up to see what they do over there restaurant-wise and pool-wise as well. I think AKV is popular for several reasons 1) it's new, 2) it appeals to those that like lots of "theming" in the decor of the resort/rooms, 3) it has a unique theme in terms of animal viewing, 4) Animal Kingdom is becoming a more popular park.