Why does autopilot continue to drive the car without someone holding the steering wheel in the first place? If the car can't drive itself without driver input,

Why does autopilot continue to drive the car without someone holding the steering wheel in the first place? If the car can't drive itself without driver input, then why isn't letting go of the steering wheel the equivalent of disengaging autopilot? Tesla's technical hubris could have killed more than just the driver.