Because Awakening's Vantage+ (or Path of Radiance's Vantage) is too OP. We're looking for something like Awakening's simple Vantage skill, or Radiant Dawn's version of Vantage.

But if I can't have Vantage, I might go with a skill like Shade (which decreases the chances of my character being attacked if there is another of my allies within the enemy's range) or just use Myst's Blinding Speed.