Bicycles aren’t very useful vehicles compared to cars

That depends on your criteria. For journeys where they are a viable option bikes are usually much cheaper, healthier, less dangerous, more efficient and cleaner than cars. Of course that doesn't include all journeys that people need to make but it does include many of them.

which is why a very small share of the US population uses them on the roads in the first place.

Somehow I doubt their lack of utility is the reason that almost nobody in the US rides bikes on the road.