>It's connected to the Internet. Every car has a SIM card now.
Maybe every new car, but the average car is 13 years old, and the OP made no clarification on whether his advice was for only new cars, or for a 2015 econobox as well.
My car is older than that and came with an embedded SIM card. Quite a few navigation consoles had "live traffic updates" (often in trial format, but sometimes "lifetime") that basically consisted of 2G clients occasionally updating traffic data along planned routes. Not quite bottom of the line at the time, but also not uncommon at that point either. It's probably slightly worse than the dedicated satnav screens people were buying back when the car was new, although neither compares to what a smartphone will expose passively from just being inside of a moving car.
There's other ways to get local traffic data, too. For instance: Traffic Message Channel, which can be broadcast with RDS on an FM station, exists.
As long as stations persist that transmit the data (it's sent over RDS), then it will continue to work. There's no subscription involved (or at least, there isn't for my car -- it works where it works, and there's no mechanism by which to pay for using it).
On the one hand, they won't be able to communicate with the home base anymore. On the other hand, they'll light up the map like a Christmas tree if someone ever turns on a stingray in their vicinity.
Most people don't know, and will never know whether their car is connected to the internet, so it's better to assume it is unless you have specific information. The app or phone you connect to the car could also be a major exfil point of this data.
Maybe every new car, but the average car is 13 years old, and the OP made no clarification on whether his advice was for only new cars, or for a 2015 econobox as well.