Who would want to pay for an additional attraction that takes up a good hour (take in consideration the time in getting to your time slot early as well as purchasing your ticket in the first place) of your precious ride time despite the fact that you have already paid a premium to enter the park in the first place?
I didn't plan to do the dungeon in the opening week, but I did it because the park was very quiet and most rides were walk on, I did all the rides plus more than what I planned to do, so I had the time to give the Dungeons a go.
My time slot was pretty much full of guest, many purchasing last minutes tickets at the entrance to the Dungeons, but I've too been told that some of the time slots have contained only 1 or 2 people in them.