Because liberals got together and deemed blacks to be the most oppressed, therefore you must say "n-word" instead. What stats are their claims based on? I dunno, but do as they say goy.
Seriously, let's use their own logic for a second, and pretend like we believe that the holocaust killed 6 million jews (probably a bullshit number, but for the sake of the argument we'll play along). Why is "jew" or "kike" not given the Voldemort treatment like "nigger"? Have more niggers been killed than jews?
The only retort SJWs usually have is, "If you can say one slur but not the other, then the second is objectively worse." Then when you ask them, "But how is it worse?" These NPCs malfunction and respond with, "Shut up altright nazi inkwell."