Board Thread:Spoilers!/@comment-24674051-20161114173607/@comment-25375217-20161115174138

There's also the concept of "color-blind casting", where directors choose to cast based on skill rather than appearance. People tend to be okay or even supportive of it when it's a non-white playing a role that should be white and call it out as inappropriate when it's the other way around, but it is still a possible explanation.