Plus, presumably, either training it on pilot inputs (and being able to map those to joystick inputs and mouse clicks) or having the user have an identical fake cockpit to play in and a camera to pick up their movements.

And, unless you wanted a simulator that only allowed perfectly normal flight, you'd have to have those airliners go through every possible situation that you wanted to reproduce: warnings, malfunctions, emergencies, pilots pushing the airliner out of its normal flight envelope, etc.