Why do the cops in this game only go after YOU?

I do love this game, but why is it that the cops will go after no one but your character? It's so annoying, because other characters in this game will rob eachother, steal cars, beat eachother to death, and gangs will shoot and kill eachother. The entire time all this stuff happens, the cops will just be walking right up and down the sidewalk as if nothing is happening. But then when your character just goes up and hits someone, the cops wont leave you alone, even if the person you hit was hitting you first. I just find it so ridiculous and annoying how the cops go after no one else, but they do in the other GTA games. I'm just curious, why exactly was it made that way? I'm sorry if this has been asked already, but I couldn't find any other topics like this.

Get busy livin', or get busy dyin.