new dungeons vs old dungeons

[Cidel]

there has to be something worth in the optional rooms.

This is the main hurdle. If there's only a chest that is in all likeliness is going to give glamour prisms or some inventory space -1 potion, the vast majority won't care; and so far that's all they've been willing to stick in most chests. Yeah, sometimes there's an accessory, but again, most players don't seem to need them and probably entered with a higher ilvl anyway.

If the devs stick some things in chests that the playerbase really wanted, like I dunno, the whole reason they're probably there, (tomestones), dungeon vouchers for some random item like PotD's or straight-up materia, then maybe then side corridors and optional areas would see frequent activity.

Back in 1.2x, the dungeons dropped several chests after the boss pending what prerequisites your group achieved. If I remember correctly, one chest only appeared if you opened every side-chest in the dungeon. There's an idea right there.