Not sure. It past years the Feb/Mar Magic Kingdom event has not sold out either. Does MK have more/enough capacity compared to the others? Is the MK event at a low DVC visit time? Is it announced so late that many members can't arrange a visit around the events either driven by life schedules or resort availability? Or did Disney increase the number of tickets they are handing out and it will be packed? Time will tell... I am hoping it is not the last.
I think it is timing and not tickets being increased. By the time it was announced there was almost no availability to book a room on points, and not everyone there will want to go anyway.