I don't think you can blame city designs. Most of them were substantially complete prior to the introduction, or at least the popular acceptance, of the automobile.
Second, people here, voluntarily or involuntarily, change jobs more often than they change homes - on the average. They cannot mandate where the office/factory will be, nor do they typically have a local choice. So, even if they are lucky enough to be able to move close to their original job, they cannot guarantee being close to their next one - and it is non-trivial and often financially impossible for many of these people to move.
Most Americans have cars or access to their family's cars. The only places where that's not the case are in the major cities, and, even there, most people have cars. There's actually a pretty small minority of people in most areas who bike to work or take public transportation - again, outside of major metropolitan areas. And, even those people who work in large cites and commute there via public transportation often live in suburbs and drive when they're not at work.
If you live 20 miles from work - or much less than that in areas with winter weather - and if the public transportation system doesn't go by your home (typical for vast majority, area-wise, of the States) then you drive, and you have no other option except to find a new job or find a new home, and most people can't really do those options.
