I disagree with you on your point of we all know the main protagonist is almost always white. There is enough media with the main protagonist with a ethnic background of African American, Mexican, Japanese, etc. I think a person's exposure or lack of exposure is due to a person's culture and their personal interests.
Some people just do not want to watch other races in media.There is a guy from a different forum who said he would feel weird if he saw a African American in a RPG game from the RPG Maker. His comment screams volumes about his lack of exposure to media with different ethic and racial groups.
I am only speaking for myself. I have seen protagonists from many different backgrounds. My first favorite white protagonist was Tommy Oliver from Power Rangers. Then, we had TJ, a black guy as the Red Turbo Ranger and leader of the Turbo rangers.