Is there much of a black population in Japan? Would be kind of weird for them to go out of their way to depict a race of people they don't have much contact with because some internet posters in America think it's insensitive or something.
Its been decades since Nintendo became a global company, more than enough time to get over any sort of lack of cultural awareness as to the diversity of their consumers in other countries. They showed enough awareness with the creation of Mii's to include a black skin tone. Can't act ignorant forever. If it helps, you can think of it in terms of Nintendo continually shafting online features in their games. Smash Run was confirmed to have no online and you can use the same sort of cultural excuse to say many of their Japanese fans are more accostomed to local multiplayer. Does that excuse them not implementing online for their Western fans? Of course not, since they even demonstrated an awareness of the problem with the implementation of the Streetpass Relay function. It would just be nice for Nintendo to add more diversity (and diversity options in the case of Animal Crossing, Fire Emblem Awakening, and Pokemon X/Y) for their games.