They won't do it because of botters.

That being said, open world mobs exist for no reason at all. Super low drop rates on crafting materials (better to use retainers), pointless xp gains, only a handful of daily hunt mobs per zone, and no actual effect on other gameplay.

It would be cool if there were repeatable hunt logs. Maybe something like the battle leves they canned, but actually involving the normal environment, and more rewarding for leveling up.