Why do people feel entitled to drive on the shoulder?

Driving on 610 today, and had stop and go traffic – it was severely backed up. I then saw three cars pass me on the right shoulder and sped off. Who da hell do these people think they are? People started closing others trying to do the same thing, and the shoulder drivers still had the nerve to get angry and upset. The entitlement and complete disregard of respect is absolutely insane. Why do people do that?