Autopilot is not an implementation of self-driving cars... You have a completely wrong understanding of this system.

It's basically cruise control that has some lane keeping abilities. If you put your (non-TACC) car in cruise control on the freeway and then ignored everything around you, you will rear end someone, and it's not cruise controls fault. If you put a lane-keeping assist car (like Tesla or others) and completely ignored the road, it will crash eventually. AutoPilot is cruise control with some lane keeping abilities, it is not self-driving. You choose when to activate it (just like cruise control), and every single time you do it tells you to pay attention and keep your hands on the wheel.