The black "population" of Japan is insignificant, as it should be (non-existent would be preferable). And that's on top of the fact that most Japanese have never even seen a non-Japanese person in real life.

Having darkies in all the media serves the purpose of brainwashing and demoralizing the population. It erodes the sense of reality that normal people have so they start thinking "maybe my instincts are wrong, and charcoal men can partake in civilization".

Besides, the stories depicted in anime and manga are usually filled with beautiful or cute characters, as well as having ideal worlds. God's charred creations are not pretty to look at, ugly doesn't sell, and perfect worlds have no room for them. If you see one of these orcs in it, and its existence is not shown to be barbaric or played for laughs, it's probably pozzed and should be avoided.