The thing is they are limiting stuff, the reason for only 3 dugeons overall is so you chose in higher levels if you want leveling doing your level dungeons or farm doing low level dungeons, which i think is fine the shared limit for all dungeons, i just think since the limit is shared it should be 5 or 6. Individuals runs for each lvl would flood the game with items like arde/pentaminons and this stuffs, in one month dungeon items would be cheaper than white items.