Ninja are the complete opposite of tanks, they move in the shadows, and aren't meant to fight toe-to-toe. That's samurai.

Anywho, I think SE designed RDM to be a hybrid. A mix between a melee and mage. Instead, the players turned it into a piss-poor healer and Refresh bot. Same thing with NIN. SE designed NIN to be a DPS with elemental Debuffs, instead the players decided to make it a piss-poor tank.

SE must have learned from this and said "Ok players, you WILL play this class/job the way we designed it. There will be no tanking abilities at all for NIN this time HAR HAR HAR". In fact, since NIN is based off ROG, I'd even go so far as to say ROG will have some enmity shedding abilities that will be passed on to the NIN, further cementing the fact that they did not design NIN to be a tank this time around.