Presumably a sizable portion of that third isn't capable of getting around on their own regardless of public transportation options.
You'll see many of wheelchair-bound people outside every day, interacting with people. I can't imagine how lonely it must be to be disabled or elderly (to where you can't drive) in a car dependent area. You'd rarely leave your house.
Walkable areas are also more liberating for children. Where I live, we have some areas that are pedestrian only, and you'll see children hanging out and playing. They can walk there from nearby homes.
The disabled, elderly and minors do ride public transportation.
That car is a big part of WHY you feel so lethargic and dread walking further than between the car and the edge of a parking lot.
Contrast with the most pedestrian friendly area I've ever seen: central Tokyo, with density so high that within a short walk of most homes there are all the services you need. I routinely see bent over grandmas that in the US would be considered incapable of traveling outside the home, calmly and slowly walking with a grocery / walker contraption holding some groceries.