Another problem with the name is that autopilots in planes and ships do exactly what the pilot programmed them to do, e.g. hold a certain course. The Tesla autopilot on the other hand tries to intelligently react to the subset of the environment which it see through it sensors, which makes it more unpredictable. I assume that pilots don't have to monitor the behaviour of the autopilot itself, whereas in a Tesla you have to do that and be ready to interfere any second. That doesn't really reduce the workload for the driver, so people just trust the system instead.