It mainly has to do with history. Someone can correct me if I'm wrong, but when the US government system was being set up, news and political education was hard to come by for those living away from the capitol. So, it seemed like a pretty logical solution at the time to pick a few people to represent the voting population of a state that actually DID have the political education. Now that we live in a time where news can be spread in under a day and most people are far more educated about politics (and in general), the system is flawed and readily taken advantage. I'm taking this off the top of my head though, there's probably more to it than just this.