My guess is that the amount of sprawl in America is a big contributor. It means there’s a higher barrier to biking, which in turn means that fewer people do it, which then means that there’s less effort put into biking infrastructure (and the sprawl also directly makes building infrastructure more expensive), and so then the people who do bike have to be more intrusive on other traffic. So then there’s tension between the drivers who end up inconvenienced by bikers, and bikers who feel threatened by drivers.