I guess what I’m getting at is that, when you watch John Wayne playing an Asian guy, do you spend the whole movie wondering why the other characters aren’t constantly asking about his skin color and facial features? Probably not, since we can easily accept that while the actor is white, the character is still Asian.
But when a black actor plays a white character in a historical piece, you want to know why everyone isn’t constantly asking about their skin color and facial features. The answer is exactly the same: the character hasn’t changed. The other characters in the film don’t see the actor, they see the character.
Well, why not indeed? Both of those could be interesting films, depending on who was involved in making them, and what they were trying to say.