Normally you wouldn't be able to get into the map room except by performing the ritual (i.e., solving the puzzle) in the rainbow room. Xambria and her crew had a similar reaction to Falkus's group. They saw the weird puzzle, solved it, then realized they'd have to solve it over and over again whenever they wanted to get into the map room. So they said "to hell with this" and just dug through the wall from the false seal room.
But what's stopping a group in the map room from just going through the southern door and into the rainbow room, bypassing the ritual?