… late 1700s, teamsters in the United States and France began hauling farm products in big wagons pulled by several pairs of horses. These wagons had no driver’s seat. Instead the driver sat on the left rear horse, so he could keep his right arm free to lash the team. Since you were sitting on the left, naturally you wanted everybody to pass on the left so you could look down and make sure you kept clear of the other guy’s wheels. Ergo, you kept to the right side of the road. The first known keep-right law in the U.S. was enacted in Pennsylvania in 1792, and in the ensuing years many states and Canadian provinces followed suit.
Safety rules etc for bikes mostly seem to be created by people who never ride bikes. For instance that idea that the back brake is the “safer” brake - it really isn’t, as of course you know, and you’re far more likely to lock up a wheel using the back brake, because the rear wheel goes light under braking.
Another example - the “rumble strips” they place on divided footpaths that have one side for bikes and one side for pedestrians. They have them aligned perpendicular to the direction of travel on the “no entry” footpath side, and parallel to the direction of travel on the bike side - presumably because they think it makes it smoother. What it actually does, of course, is provide a tramline effect that can grab your wheel or make it skid if you cross at a slightly oblique angle. It’s much safer to detour across the perpendicular ridges.