it’s not a mystery anyone can look it up now on line but the story is and has been that teamsters hauling loads on horse drawn carts use to sit on the rear left horse and they stayed to the right side so the could make sure they didn’t knock carts with other carts passing in the opposite direction when they started siting on the carts they stayed with the same set up and it just came down the line over time that way I have no idea why the few that drive on the wrong side do. I wonder if they have more side swiping incidents?