People are afraid of progress and change. Its that simple. In the past several big groups of the time colabated together to make music and stop the hate. Anthrax & Public Enemy, RUN DMC & Aerosmith, Ice-T in Body Count, countless soundtracks and concept albums.
When a new group which is clearly influenced by both genres gets big, it gets hated on for doing so or gets a demeaning label such Nu-Metal. Lately it has become fashionable to hate so called boyband groups like Linkin Park which may or may not be a studio exec's creation.