Because there are changes which will make the multistage dungeons a part of the quests with plot. You have to accept a quest before you are allowed to fight there.
Unfortunately I dont think they are active yet, they are probably testing them in alfa, so please be patient till they are done...
i think they are active but quest description is not complete. every story line have about 9-11 quests by now and like i see there is three stoly lines wich should works if are implemented
in haroda land's you need to kill
in examples
in silent gulch.
first quest for story line in hope village is in boar's head
dont remember wher is dawn hill but first quest in this province is to kill 5 wolfs in this dungeon