Or they could name it something else (bit late), or just have the mist go across in clouds, sometimes obscuring your vision. But periodically let you see the view around you - it really is worth seeing, probably my most favourite looking of the biomes.

Or if anyone had any imagination at all, there could be reasons. Off the top of my head, it's called the mistlands because it was shrouded in an impenetrable mist for centuries/eons/since last Tuesday - but now after killing yaggy, it's lifted and you can venture in.