Why do people talk loudly on their cell phones in public?

Why do people think you are interested in their phone conversation? They act like there is no one in the room but them. Do they know that they don't have to shout across the room for the person on the other end of the conversation to hear them?  Do they know that the rest of us do not find their conversation interesting? Do they know about noise pollution? That such a thing exists? Listen people, next time you are in a room with others and want to have a phone conversation, resist the urge while still in the room.