Eh, it's part of it, but not the whole story. Utah is a pretty close place and it has a lot of sprawl (traffic isn't too bad though). So many things have changed in the last half-century or so that I don't think you can point to any one thing as the cause. Even in a city with a lot of sprawl you likely have a lot more people you are within a 10 minute walk of than someone in a mid-size town is within a 10 minute drive of, it's just hard to meet those people because most people stay within their existing bubbles unless some event shakes up their life (breakup, job change, moving, etc.)