The lower level dungeons teach some decent mechanics. Ranged trash that won't move with pulls, DoTs that need dispelled, bosses with weird mechanics at different stages of the fight, etc. Unlike the slopfest going on in PotD, you can sorta kinda learn to play your class/job in lower level dungeons, so making them easier does not much except further dumb down and erode the current overall skill level of the playerbase.

Not sure anyone really wants that.