Where is it written "Thou shalt drive in the middle lane"? I get a little tired of driving on the highway and streets with slow cars in the middle lane (or worse yet, the left hand lane). Many states, including the one I live in, have laws along the lines of "stay right except to pass." My state even posts signs says such on the highway.
I've been tempted to mount a camera on my dash to record the gyrations that I have to go through to get through traffic. Mind you, I don't have to be speeding to have this problem. People are comfortable driving below the speed limit in every lane (at the same time). Slow cars in the middle lane, slow cars in the left lane, so I wind up spending a lot of time in the right lane. That is, until I find the 1 percent who is a slow car and knows to drive in the right lane. Then I'm having to weave through the middle and left lane to get around that car.
I think that I've figured out why people tend to stay in the center lane. They don't like the right lane as cars entering and exiting the road would use that one. They then leave the left lane for passing. This seems like a reasonable explanation if you ignore the ability of their car to change lanes to go around cars exiting or give room to a car entering the road.