The demand for stories which fit this narrative outstrip the supply. The same thing can be seen with various 'hate crimes' which are eventually revealed as hoaxes. The media - and the public - are strangely desperate for this bigoted world to exist - because they can feel more noble fighting it.
I'm guessing it has something to do with all the ideological refugees, in academia and the media, from the 60s and 70s who are fighting battles that are long over.