There is a very simple reason this phenomenon is so institutionalized; it's because people who create fiction, be it books, movies, or videogames, will always, and are often trained
to in college, create said fiction by grounding it in things they know.
Ever wonder why nearly every television show and movie takes place in New York or Los Angeles? Nearly everyone who writes them lives in New York or Los Angeles. They know what it's like being in these places because they're in them every day. You can look up a Wikipedia article on Albany, NY and learn about it, but you won't know what it's like to live
there the same way you do with your actual home.
Why do characters in video games seem to have such a slant on represented demographics? Because most of the people who make videogames are middle-class white men.
Giant flaming queer that I am, I've been wishing for a decent game with a believably written gay protagonist for years, but I don't hold out much hope. How do you write a gay character? How do you write a gay character in a relationship? Simple answer; the same way you write a straight character, albiet accounting for the fact that he likes dudes instead of chicks, and in a relationship, the dynamics said chick brings are non-existent, because neither of them will magically start acting like a woman.
Bioware is a good example of what happens when a dev team is aware of how this works; being aware of it doesn't actually make it change in good ways. There's no gay option for a male character in Mass Effect because they were afraid to write it without having any gay guys on-staff to proof-read it, and this has apparently changed for the sequel. To me, needing this is absurd, because I don't have to put effort into wrapping my brain around how to do it. The devs who are perfectly straight can listen to their co-worker saying what I just said about how to do it right until they're all blue in the face, though, and they'll never truly understand it not because they're psycho racist skinjobs, but because they just simply can't relate.
Same goes for other demographics, and hence, "write what you know." It's not even unreasonable; I'd much rather play a game that represents demographics the dev team can relate to and thus represent properly rather than watching them turn other
demographics into representations of their common stereotypes, which, no matter how much effort they put into honest "research," is how it's going to come off. Research just doesn't help very much with this. In point of fact, most writers simply don't want
to write about demographics they don't belong to.
If you want more blacks and latinos in games, convince more blacks and latinos to take up game development as a career.
NOT THE BEES! NOT THE BEES THEY'RE IN MY EYES