You don’t need a data plan to call emergency services. Any protocol-compatible device can dial 911/112/etc. for free.
This is why in remote areas your phone may say “Emergency Calls Only”. Your carrier isn’t available, but someone else’s is and they are legally obligated to route emergency calls.
Of course if your car has a modem and a computer, adding a data plan isn’t a huge leap. But it’s a recurring expense and plenty of cars sold today do not have internet connectivity, at least on the cheaper side.