Much of the US is not dense, so many people have to drive to get places. In my experience, most areas don’t have the infrastructure for cars + pedestrians + cyclists, let alone just cars + pedestrians. The few places that do intermingle all three do so in a way which is very overwhelming for drivers. Cyclists also tend to travel either too slow for cars to maneuver around or too fast for cars to notice them coming. Like motorcycles, their small size also makes them hard to notice or keep track of while driving, and they don’t make the volume of noise that motorcycles do which helps with noticing them.