If sexual attraction is all about releasing and receiving pheromones (iirc) then maybe it is that phermones released vary depending on your genetics and your particular receptors just don't process the pheromones created by certain ethnicities? I don't know... Everyone who experiences sexual attraction has that attraction to different kinds of people... some people they respond to and others they don't... that's what makes the experience varied... so perhaps there is some biological basis in that rather than purely mental. I don't know, I'm just theorising.