...except if said family has kids of the age that they need
car seats, which are a pain in the ass to install correctly; ripping them out and putting them back in twice a day is both ridiculous and unsafe. And you can't realistically even have shared cars with pre-installed car seats, because they need to be adjusted all the frigging time as the kid grows.
FWIW, neither my wife or I had ever owned a car, we managed just fine with public transport and car-sharing. But once the baby came along, we pretty much had to buy a car.