Tesla warned that driver still should be alert, they implemented warning so driver would keep hands on the wheel etc. NHTSA reported that driver had 7 seconds to react on the truck. In a spin situation because of some bug autopilot would create the problematic situation itself, even if driver will be paying attention to the road.

Yeah, the problem was letting people get the expectation that it was an autopilot when it wasn't. Decades of Human Factors research in aviation had already established that people can't maintain focus on a sufficiently-monotonous task.