The United States was still very much early in its development when motor vehicles arrived. So, there was still great possibility of planning and building towns, cities, workplaces, etc., with the car in mind. Just to provide some contrast, in Europe, there was less possibility for complete bottom-up development of these things by the time cars came onto the scene.
So, now cars very important for intercity travel in the United States. Distances are often not so amenable to biking as, say, in Europe. So, bikes are more often just toys here.