I would like this topic to be an overall discussion between the pros and cons of toughness and vitality, and how they can help - both alone and in combination - mitigate damage and increase survivability for your character.
In GW1 (and feel free to correct me if I'm wrong, GW vets), I was of the understanding that while you couldn't neglect your health, armor provided (overall) a better bang for your buck.
toughness doesn't reduce condition damage. That's the most likely reason.
But toughness does make each point of health worth much more, which is important because vitality increase isn't optimized unless you also somewhat invest in healing power and sport a heal that scales well with healing power.
It really comes down to the situation that you are in and personal preference.