Someone complaining about how this kept imposing Japanese culture on other-worlders should also complain about why Superman/Supergirl are white Caucasians despite being aliens.
I mean, the reason is painfully obvious, and to be frank, virtually inevitable: It adheres to the story creator's own background. If the creator is a white American, then a major part of the story will be centered around his/her white American background. If he/she is Japanese, then, well, there's bound to be a lot of Japanese influence in there.
This is also why the Hobbits in Tolkien's lore love their tea time. So even someone like J.R.R. Tolkien couldn't escape this trap. Go figure.