Quote from: Ghostcrawler (Source)
We think mages are still having mana problems and don't want to reduce Evocation's cooldown anymore. Nor do we want to buff mage armor too much more or using e.g. molten armor seems pointless.
Instead, we reduced the mana cost on Fireball, Frostbolt, Frostfire Bolt, Arcane Blast, Arcane Missiles, and Arcane Explosion.