If you have a sizable populace willing to garrote you if your award nominations do not include a large enough representation of minority populaces, regardless of how movies, actors, directors, screenwriters, and anyone else actually performs in any given category (which, I believe, is the main point of an award), the incentive for including an equalized representation across all award categories far outweighs the benefit of awarding based on merit.

That is the evidence you asked for, you're welcome. It's not a white / non-white question at all, as you can see.