Why do Ninja and Monk use different gear?

[Felis]

Physical dps tables are way too bloated, where tanks, casters and healers get to share gear. I think monk and drg should share gear and nin with brd/mch UNLESS there's a specific reason they shouldn't.

Different amount of main stats. DRG gear have more def than MNK gear. This would mean keep the stats how they are and buff the monk with more def or change the stats and nerf DRG with less def.
Also different favourite 2nd stats.