Too late for the dungeon core talk, so probably talking to the void here, but I feel the same, I think a dungeon core story is quite hard to write as at its core (unintended) it's a story with only one character and no scenery change, so writers feel the need to include characters that can go farther than the main.
I actually got around writing the outline for one a few months ago, but deleted it on a moody day, now I'm regreting. Let it be a lesson to never delete your writing, even for how shit it may be.