Answering that question should be easy. Mostly, I think it's because the majority of everything we do, is realistic. I mean, we obviously life in the real life. Most everything we see on TV was made using real life people and objects. Most things that don't, are intended for a younger audience, or are very stylized in themselves. It's natural to transfer that into the game world as well. Besides, it's always been harder to make something super-realistic rather than stylized, and everyone likes a challenge.
People strive for realism because we like things to be real. If nothing else, it at least helps a lot with the immersion.