Because some classes have more burst than others. Some classes just don't even have burst at all.
You can't just nerf burst, you have to look at the classes who are the major offenders of burst:
Warriors, BM Hunters, Ferals, Mages, Warlocks
DKs are borderline
That's over half the classes in the game you realize.
In a world where healers can heal someone from 10% to full in a split second, the counter is burst.
Working as intended imo.
But that has got to be the worst game design philosophy I've ever seen. How is it fun to be ping ponging between 1% and 100%?
What ever happened to the "wounded state" ideal that was intended for PvP in Cataclysm??