I figure the best way to understand it is as an incremental set of small choices that each seemed like a good idea at the time. Fundamentally people like traveling in cars, and hate traffic. These two things pretty easily make the case as the underlying principals of everything driving car-centered city design today- parking minimums, wider & wider roads, cannibalizing trolley track, marginalization of pedestrian & bicyclists, etc. Then you begin to get second order effects- because everyone drives, things like storefront design codes are just inherently designed for the gaze of the automobile driver. (That one was an eye-opener for some of the subtle effects of car-centric worldview)