As for Duty Finder and Duty Roulette, that's an example of
gameplay and story segregation, in that story-wise you're not going back to the same dungeon over and over again, the story treats it that you only ever enter a dungeon once and then never again (the only time you return to a dungeon is it's 'hard mode', which is why HM versions are set afterwards and show physical changes to the dungeon's environment). DF is nothing but a gameplay mechanic with no connections to the storyline of the game at all.