Purple flame walls in dungeons

Is there any legitimate purpose for the purple flame walls that pop up in dungeons? I assume they exist to lock boss rooms once you pull, but why don’t they disappear after? Why are there only teleports on one side of the wall, or why doesn’t another one spawn after downing the boss?

Trying to do mokoko seed clears of dungeons, especially considering there are secret paths that require you to kill every mob, when this feature exists is incredibly frustrating. If you go too far or miss a seed, you’re forced to just song of escape and clear the entire dungeon over again.

It’s a minor thing, but I don’t understand why there’s literal gatekeeping access to a dungeon that you’ve just finished clearing. Alternatively, why isn’t there an option to teleport back to the dungeon’s start (at least after completing it) that doesn’t force a reset?

It seems counterintuitive that so much of the game is based in both completion and zone exploration, yet you can’t explore an instance after completing it, only before.