We're a species of motile organisms. Not only do we have legs, to not use them is actively unhealthy. If we're going to just sit in chairs all the time, we might as well get rid of all this useless leg biomass and redesign our houses and offices accordingly.
It's worse than this though, because that's just the physical dimension to our existence. The car is a mediating apparatus that alienates man from his social field. Man is a social animal, and needs sociality to maintain mental stability. If there's always a car between you and members of your own species, intersubjective experiences will simply occur less, which is exactly what happened when everyone got one.