Reason nr. 1. Racism!
Japanese are very very racist and would show how they feel superior at every chanse they get.
Nr. 2. Japanese are not polite and will not help you unless: they have something to gain, or it is a social setting where they have to act a certain way.
Nr. 3. No matter who you are and from where you are, if you are not Japanese in Japan you are a second class citizen. Good luck getting in a Japanese night club if you are not escorted by Japanese. Good luck renting a place.
I mean it is no coincidence Japan is they only country to ever get nuked..... Twice!
Also every neighbor country to Japan hates Japan