Hilarious article title 
I think one reason that Japanese men don’t pickup on the few Western women who are in Japan is that the standard of beauty for the majority of Japanese men is Japanese women, not white women. Look at the women who are on the covers of magazines and TV and movie shows. Not white. Asian. Japanese.
Yes, there are exceptions to every rule.
The main reason why Japanese men do not appear to be giving off signals is that many assume Western women are only interested in dating Western men. Big, muscular, “manly” men are usually the ones adored by the media in any country and, on the whole, Japanese men simply are not like that, and they know it. They assume they are not what a Western woman would be looking for.
Many also feel a little bit intimidated by foreign women: a large number of Japanese people develop impressions of foreigners based on American movies. Women in these movies are often independent, confident, articulate about their opinions and enthusiastic participants in bedroom activities.
Everything you always wanted to know about Japanese men who are afraid to ask [weekender.co.jp]