I lack the cultural insight but from far across the seas here it seems that using the n-word is borderline illegal unlike bitch/hoe. Didn't kramer get crucified for using that word? Do you think he would have gotten the same reaction if he had used the words you mentioned? (His entire career went kaput after all).
Bitch/hoe are terms that the politically powerful majority use to keep a minority in check. The people who use bitch/hoe are already on the skirts of society. The people who used nigger casually included powerful people of all stripes, right up to senators (and probably a few presidents). Bitch/hoe was never seen as something that a 'respectable person' would legitimately say.
