"So what?" Well unfortunately there was cross traffic on a divided stretch of Florida highway.
And now you realize why maybe autopilot in this location would not be 100% effective or would mean you'd still need to be vigilant and watch for unsupported situations.
Also if a semi turns right in front of you, autopilot or no autopilot. you have to be on your game and you still might get into an accident.
I understand your line of thinking because it's quite common and it seems to be contagious in the news media. But let me ask you if you set cruise control on a normal car and get into an accident are you going to blame that when you hit something or drives off a curve? No, because you understand the limitations and that it's outside the spec. The same is true with Tesla Autopilot.
There are situations that it was designed for which are well known and documented, but there are also situations it was not designed for. What happens if an elephant falls out of the sky? Should autopilot detect the falling elephant and brake in time? Are we going to blame Autopilot or Tesla that it failed to recognize a falling elephant? You understand that this situation is preposterous, but so is asking why it didn't do something it wasn't designed for.
It's not like that feature isn't coming. We already know it'll be here in 2018. The point is, it's not a feature now and, if used appropriately, Autopilot will save more lives than without it.