A plane autopilot is supposed to be capable of flying the plane unattended and handing over control in an orderly, controlled fashion before critical problems arise [1]. A ships autopilot is expected to do the same. The same should be expected from a car autopilot. The fact that the environment is much much simpler for planes and ships doesn't change the fundamental expectation. As long as car autopilots are not capable of fulfilling the expectation that they can autonomously and safely control a car in a given real-worlds environment with other participant they should not be marketed as autopilots. They're driving assist programs.

[1] there are examples where this did not happen, but they're considered a failure.