If WAR can gain heal from AoE why DRK can't gain MP in the same way?

If WAR can gain heal from AoE why DRK can't gain MP in the same way?

it is not logical.. 30 second recast time that heal for 100% hp

and dark knight can't gain mana on AoE for maximizing damage?

can we got explanation?

Probably because it becomes a damage gain while all the healing on the planet doesnt make the addpacks go any faster.