The trope is stupid but people are generally idiots and or lack self-awareness and the ability to truly analyze their own thoughts and behaviors, thus we have really stupid arguments about race where apparently NOTHING is racist despite the overwhelming amount of anecdotal and statistical evidence. People are too fucking dumb to realize that the vast, vast, vast majority of racist acts in modern society come from those who don't think they are racist, or that their action is racist. It exists on a more "unconscious" , "subtle conditioning" level. If tomorrow all media started having white/lighter characters as villains every time, and darker characters as righteous, you would all immediately notice it. If it started to affect how they were thought of, ability to get jobs, etc, many white people would quickly change their guns on stuff like this. But they don't get it, and probably don't even have the capacity to get it.