Motorcycle Wave

I have always been puzzled by the motorcycle wave. I followed these two guys from work for about 25 miles and of course they did the extend the hand out to the side wave. I'm pretty sure they did not know the other 6 or 7 bikes they passed but they waved. I consider myself a pretty nice and friendly guy but you don't see me or other cars rolling down our windows and waving at every car that drives by. Even when I pass a similiar make and model car as mine. I have had my motorcycle endorsement for years and rode a street bike, but don't remember anywhere in the manual that states I should wave at every bike I come in contact with. Our state just passed a law in which I can not hold a phone up to my ear while I drive, and I have four wheels (for safety reasons they say). I'm thinking maybe our state will make it illegal for motorcycles to wave at each other. Just my thoughts.