They have rewards for tanks including extra points/gil/mount.

Yet.. there are still wait times. You know why? No matter what Yoshi comes up with to get more tanks, there will never be enough tanks.
This is a dilemma in every MMO I've played it. People just simply don't like to tank.

This is why I level a tank. Also, I do runs with my FC for my DPS needs. Heck. Put up a party finder for it.

Want to be DPS- you have to deal with the wait times. Yoshi can't force people who don't want to tank, to tank.