The thing with walking is that it's very much a "use it or lose it" thing; people who never owned cars are much more likely to keep walking.
I know a lot of broke people who live within less than a two minute walk of a bus stop and could not possibly afford a car. You might want to consider how the built environment has dictated your choices.
Also on the point of cost, cars are incredibly expensive, especially in the US where everyone seems to have massive vehicles. If you live without one, in a pedestrian friendly area you'd find the costs of using a bus or subway would be a small fraction of your car costs.
Actually cars are dirt cheap in the US compared to Europe. Taxes are low, second hand cars can be had for basically nothing, and gas is cheap.
There's also a bit of good fortune involved. I was young, single, and healthy. But I'm older now, and there are times when I simply cannot afford to use public transit or walk. If you get the flu, you don't even have the choice; walking fifteen minutes to get medicine or food is agony. And you always have to walk fifteen minutes, just to get to the transit spot. You feel the weather a lot more as you age; a brisk rain shower is rougher on you at 40 than at 20.
And come on, what can be more totalitarian than restricting the ability of people to move beyond a tiny radius apart from communal vehicles that can be shut down on a whim?