Many of the current cars are 100% drive by wire (ECU/power brakes/electric power steering), but that doesn't mean anything.

Probably quite a good part of the $hundred of millions price of a passenger plane is the autopilot (even 1% means $1M). And even at $1M/plane, 99% of a plane's autopilot works because it assumes that the current plane is the only one in a large vicinity of a point in space. This is assured by a centralized third party (control tower) that is not really automated but a very stressful human job (that's why the air traffic controllers are well paid). This is not the case with cars - in this case, most of the work being done is having each of the individual cars detect, with complex but not very good sensors and software, what is around them, in a swarm of other moving objects that do not communicate.