Don't get me wrong, I find aircraft automation impressive. But there is a massive human workforce that makes it possible for the cabin crew to run planes on autopilot. There's a mountain of rigid regulations, licensing and certifications that control every part of that workforce. Every part of each aircraft. Every piece of communication.
That's not how the roads work.
We just don‘t place them inside the aircraft.
I would also add that aircraft are monitored by ground control stations, while cars are controlled by the driver alone.
That's only if nothing goes wrong. On the other hand, if the airplane I'm in loses both its engines and has to land on the Hudson River[1], I'd much prefer to have an experienced pilot and copilot in the cockpit.
(Note that it's not fully autonomous, the pilots still need to do quite a few things like lower flaps, extend the landing gear, ....