It's because we're not warriors, or what looks like paladins now.
Warrior T11
2-Piece = Bloodthirst and mortal strike Damage +5%
4-piece = stacking 3% attack power buff
DK T11
2-Piece = Frost Strike and Death Coil Crit +5%
4-piece = stacking 3% attack power buff
Warrior T12
2-piece = All shouts give Physical Damage +10% for 12 seconds
4-piece = Mortal Strike and Raging Blow has 30% chance to do 100% weapon damage as fire
DK T12
2-piece = Horn of Winter gives 3/5ths of 1 runic power per second for 2 minutes <---Worst bonus ever
4-piece = Frost and Scourge Strikes do 6% extra damage as fire damage.
Now it's going to be paladins with their guaranteed 1 holy power for every judgement they do plus 12% increased damage with zealotry.
My question to blizzard would be, why not just let us have a damage buff while stuff like unholy frenzy or pillar of frost is up? It's pretty much the same thing.