It's weird to have the same rules when there are several orders of magnitude difference in manueverability, maximum damage possible, and visibility between the two modes. Imagine if pedestrians had to follow all the same rules as cars. Or everyone in an electric wheelchair. It wouldn't make sense.

I think the point is they have to follow the rules of the road because they are allowed in the road. Pedestrians, wheelchairs, etc can go on the sidewalk and be safe from traffic (one hopes).

Though it depends on the state and in my experience there are typically some differences, such as bikes are required to share the lane.