> I'm finding it challenging to reconcile your personal example with the images of the smashed windshield

Really? It seems fairly obvious to me. The sensors are in the front of the car, lower down. So anything on the ground in front of the car registers as an obstacle and the car stops. Such as a small step.

The front of this trailer (they keep referring to it as the back, but it's clearly the front) was too high off the ground to register as an obstacle. You'll note that the front of the car has plenty room - there's nothing blocking it - but the windscreen doesn't!

So it needs to be fixed; you could imagine a Tesla running into, say, a small truck with timber sticking out the back when the speed was low enough that the safe distance between vehicles was small. But it hardly seems life-threatening in any way.