I actually read an interesting article about this a few weeks ago. In culture, there are phenomena called markedness and unmarkedness.
Take a smiley face. A circle, two dots for eyes, and a smile, no more. This is our unmarked example. If you live in America, you will probably view the smiley face as a white male. If you live in Japan, you are likely to notice it as Japanese. When something is basic and unmarked, we tend to defer it to our status quo, hence why Americans look at anime characters and see whites, and Japanese look and see asians. Note that I didn't say that whites see whites and vice versa, as studies show that minorities in a certain culture will still typically view the unmarked as the main stay of that culture.
Markedness is as it would imply, marks to distinguish deviations from the status quo. If we were to change our smiley face to have slanty eyes, most Americans would ***** about its racist resembelence, but they would still undoubtedly see that its meant to portray an asian.
Anime characters are typically unmarked for racial bits, so the viewer will tend to associate it with the status quo. Hell, If you showed an anime to a tribe of black people who never saw any white men, I'm pretty sure even they'd see the anime characters as black.