It's all business in the left hand lane

If only those words were true.  Why do people insist on driving in the left hand lane when there is other traffic moving faster than they are?  Does it make them any less of a person if people pass them?  Do they think they will never get back into the left hand lane and be stuck behind a truck with a trailer containing a refrigerator doing 70km in a 100km zone?  I am convinced, through no scientific evidence, that the people going slowly in the left hand lane are responsible for 75% of the traffic tie-ups.  As I said, absolutely no evidence of this fact, it just feels right.