It's an issue that is especially bad with the US' low population density in most places. We've adapted to needing cars to get anywhere; it's a problem that feeds itself. City planning ends up lacking when it comes to pedestrians because we're conditioned to drive everywhere, which makes us drive places even more.

In San Francisco you have excellent pedestrian and public transport--why not walk anywhere? Yet if you go just 20 minutes south to Daly City you'll find streets without sidewalks, sidewalks that just end in the middle of a long stretch of road, and sidewalks connected to nothing going to nothing. Suburban sprawls make the matter worse, and even worse as you get away from major cities.

I was wondering why it seemed so much colder here in southern California with 50 degree temperatures than it did when I was in Kentucky at freezing temperatures a few weeks ago. The answer is actually pretty related to walking: here I'll walk to work and endure the cold. In Kentucky, you never even spend any appreciable amount of time outside to notice the cold-- you go from your climate-controlled house to your climate-controlled car to your climate-controlled destination. It works the same in the extreme heat of Arizona in the summer.

Even if temperature weren't a factor, there was no where in KY that could really be walked to in any reasonable manner. The city layout didn't allow it, nor was the infrastructure there for it.