My city is not walkable (most of it).
Also, due to chronic illness, I don't have the spoons to walk everywhere and stand in the heat/cold waiting for a bus. I had to walk everywhere, and I took the bus, etc, when I lived in the burbs. I DO NOT have the spoons to do that anymore.
Also, not all cities are walkable (e.g., there are no sidewalks, and it's too dangerous to walk in the street), and rural areas require a car because it's 2+ miles before you get into town.