The fact that you could shoot a nearly infinite clip made it a trolling weapon in Crucible as well as a lawnmower in PvE. By nerfing the Black Hammer, they're balancing Crucible matches against people who own it, and making it so that you have to make a battle plan in PvE instead of going in guns blazing. They're finally turning Destiny into a game that requires skill and stretegy, and not just a shooting gallery where the only requirement is half a million ammo synthesis...