Y'know... I live in the suburbs and you'll be surprised how many amenities are walkable, yet everyone still prefers to drive. At the end of the day, people are just lazy as fuck. Unless there's a good carrot (or stick) that'll motivate them enough - looking good doesn't seem to be a good enough carrot, and deteriorating health doesn't seem to be a big enough stick - they won't change.

Perhaps a fat tax coupled with a staying healthy tax return might help.