Because it still basically does what’s they said. The only new advent for the autopilot system besides maintaining speed, heading, and altitude is the ability to use and set a GPS heading, and waypoints (for the purposes of this conversation). It will absolutely still fly into a mountain if not for other collision avoidance systems. Your average 737 or A320 is not going to spontaneously change course just because of the elevation of the ground below it changed. But you can program other systems in the plane to know to avoid a specific flight path because there is a known hazard. I want you to understand that we know a mountain is there. They don’t love around much in short periods of times. Cars and pedestrians are another story entirely.

There’s a reasons we still have air traffic controllers and even then pilots and air traffic control aren’t infallible and they have way more systems to make flying safe than the average car (yes even the average Tesla).