In walking cities you interact with the city itself -- you can stop and look at things closely, walk into a small store you've never noticed before, run into a friend and chat, or pause and just people watch.
In car cities everything's far off and viewed through glass, your only interaction being which direction you point your car and how fast it moves. And becoming distracted by something interesting causes expensive and dangerous accidents. Plus, driving is inherently frustrating and exhausting, in my experience, especially when compared to walking which is at least a nice bit of exercise. You just want to be where you're going and WHY IS THERE ALL OF THIS TRAFFIC?