Maybe the drivers were paying attention and did watch as the car crashed into the stationary object. Maybe they were led to believe that the car would take some action because "it has avoided things before, I don't know why it didn't stop this time".
If they trust the car to avoid things because "OMG, it is amazing, almost like it's seeing through several cars ahead, I can go hands-free and it relieves me of all the stress of driving", then they are going to be surprised when it fails to avoid things, and they are mostly going to just let it crash because it happened too quickly to figure out that THIS TIME it wasn't going to help.
It's both their fault for trusting it, and the system's fault for being so useless that it can't even tell them "HEY, you know there's a stationary object up here that I'M NOT GOING TO STOP FOR, because I don't stop for stationary objects. In fact, because the car ahead of you moved out of the way I'M GOING TO SPEED UP and just ram that thing. I see it, but I don't care, because you should have read the manual better. I'm not even going to beep or anything. If I stopped here I might get rear-ended and I don't want that, so I'll just ram you into it".