planar pendant for rogues

[Bless]

Warriors - potent self-heal (HoT) + dmg buff //+ 3x 25% HP crystals + 50 armor (healing stacks, armor buff doesn't stack).
Sorcerers - potent self-buff (dmg-primary) //+ 3x dmg crystals + mana (both effects stack).
Rogues - okay self-buff (crit-dodge-primary) //+ 3x crit/dodge crystals (that don't stack).

Why do mage buffs stack?