I think because of don't show where is shortcut and make buying map a little useless for player if they finish whole dungeon and know there is nomore stuff to get. I think this mechanic with some change can use in new games to.In 7th Dragon on the DS you can't really map any of the dungeons, but you have to look for it either inside the dungeon on a chest or ocassionaly on the shop from the closest town, it actually encourages town exploration and checking around each part of the dungeon. The only downside is that the maps don't really show you where the shortcut is if you want to leave the dungeon when you are done exploring.
As you said now I remember evil within 1. You don't have any map for any chapter.instead you collect map fragment for a big map in Safe room in sebastian mind. it was cool to collect and get all things. But some map fragment was a nonsense, and they always find in weird place. I find one behind a boss room and see someone find one on a desk! They are so easy to miss.