I suggest to introduce dungeons decaying. Currently only lairs decay, while dungeons stay forever. With dungeons being limited in number for the whole world, that makes people living outside of central continent and new players to never ever see them.
At this point of the world all the underground dungeons are spawned and locked in someone's mines, who obviously don't clear them for whatever reason and new ones wont spawn.
While Ant/Bee/Beaver dungeons can be found overworld, they are typically somewhere in starting continent, or walled in by people. (I have seen plots, where dungeons are used as decorations, behind defenses).
There is no reason not to introduce decay to them.