its the new thing they are trying, integrating dungeons into main story. probably cause DLC dungeons are not selling very well (though honestly, its not becasue they are not tying into a new story, ZoS >_>) all the DLC dungeons have a story to them, though. Wrathstone was just first time when that story is directly connected to the chapter and subsequent adventure DLC. oh and scalebreaker dungeons on at least normal, are required to unlock one of the wings inside a lunar champion home, you get after doing Elsweyr's main story.