When I arrived in Arkansas, I wondered why the drivers gave me sooo much room; much more than was necessary by my California sensibilities. Reading the driver's manual gave me a clue.
"Give extra space to pedestrians or bicycles, especially children. They can move into
your path quickly and without warning. Do not share a lane with a pedestrian or
bicyclist. Wait until it is safe to pass in the adjoining lane."
While technically, it says share the road, it also lumps bicycles with pedestrians and tells the driver to treat them as children, and tells the driver that they must not share the lane.