Really, why do you know that?

I would expect a car to have tons of code.

Think of all the functions...

Engine management, Engine monitoring, Powertrain control, Emissions, Diagnostics, Infotainment, Satnav, Climate Control, Traction Control, ABS, Anti-collision radar, Cruise control, Lane keeping, Backup camera, Parking sensors...

Now keep in mind that these hundreds of components exist in many many possible configurations so the system needs to handle having certain hardware available or not, and also handle a multitude of failure modes gracefully.

Perhaps because cars ran just fine (albeit with fewer features) for a long time with zero lines of code.

So did horses without any gasoline

Yeah, and so did banks, and so did airplanes.

So the more important question is: did adding software improve things (enough to be worth the “cost”)?

With cars, there are certainly many things where it did improve things: satnav, reverse camera, traction control etc, but also some where it made a perfectly working system worse (ie the “fixed” something that wasn’t broken): touchscreen dashboards.

Because my car has exactly zero lines of code and it runs just fine.

I guess in cars they use less (public) librarys because of safety. So there own libs are included in LOC. If you look at a modern Microsoft licence, they list tons of used open source libs in there products. I guess if you include all the librarys, the LOC number should be much higher.