Do you seriously think it's easier for a 80-year-old to hop in a car to go somewhere than walk 10 minutes to the store in a more compact city or take the bus?
Plus, look at the Netherlands, geriatric people who've biked their whole lives and maintained good physical shape have no problem continuing to bike.
Walking to a store everyday to buy only their daily necessities would end up costing them a lot more than if they were buying a bunch of what they need in bulk, and nobody ( especially an elderly person) is going to walk home carrying around their items in bulk sizes.
Even for people lucky enough to live in those rare areas where you can walk to a grocery store, it's extremely useful to have access to a car you can fill up with large items.