Some people (like me) see games as a chance to role-play, to be something you could never do in real life. I like to take it seriously as it is far more immersive if you do so. (For instance, I liked to drive safely in a game like LA Noire whereas my brother preferred to run down hundreds of people on the sidewalk.)
A lot of it is down to the fact that when most people play a game, they just want to have fun, they don't want to be patient, they don't have the time. We all know that its not real and that our actions in a game don't hurt anyone, so most people don't care or aren't patient enough to be 'civilised' and normal. Instead its just a chance to mess around and have fun. But like I said, I personally prefer to have a slightly more serious gaming experience. Whereas my brother just wants to mess about, run people over and watch the funny ragdoll physics. But either way is fine, gaming is after all, a personalised entertainment experience, as opposed to a movie or TV show.