<captain OBVIOUS=""> Because the demographic consists mostly of white men who like to project themselves onto blank characters. Not to mention the North American continent is generally saturated in the idea of Eurocentricism, and most people don't notice because it's the norm. Also, people don't take too kindly to stuff that's too different. </captain>
I can understand where your argument is coming from. However, there are plenty of games with strong leads characters aren't white/male/etc.: Lee Everett: The Walking Dead Page: Fable III (while not a lead character, her personality was strong and she was a major female role in the series) Faith: Mirror's Edge The Elder Scrolls lets you create your own character. That's super not rascist/sexist.
One game, though, I have a problem with, is CoD. Every guy is basically white, and women are not represented in the military. Even in the Black Ops 2 trailer, the narrator says "only men can finish the job" It's not that hard to say mankind...
There are a lot of points that can be argued for your argument. It's not just "Yes, games are racist" or "No, they're not"
There's not going to be many games that say "Okay guys let's drop our guns and play tag." The major reason being that a game like that isn't really marketable. Games like Halo, Assassin's Creed, Call of Duty, and Mass Effect are marketed for their action.
Faith, from Mirror's Edge, was a runner (kind of like the bike people from Premium Rush) in a city with tight government control. She's willing to risk her life to prove her sister's innocence (a sister who is a police officer in this tight government) for a murder she didn't commit. For me, Faith is one of the strongest female characters I've ever seen in a game.