How about audible nags? How about flashing white lights on the display? How about gradually slowing the car down until you give tactical feedback proving you are in control? Tesla does a lot of things to coerce drivers to pay attention. If you check out TMC, you'll see lots of people complaining about how paternalistic and "naggy" the system is, even for those who use it properly.
I am continually surprised by how little emphasis there is on personal responsibility when this community discusses an L2 system such as Autopilot. According to both the law and the operating manual, the driver is in control at all times. Tesla warns you of this every time you turn it on. Yes, there are enough bad drivers out there that Tesla is wise to implement habit-forming nags; but drivers also need to take responsibility for how they use (and abuse) these systems. Nobody would pass the buck to cruise control for a driver who set it to 65 and then plowed into something in a moment of distraction. All due respect to the victim here -- and I feel absolutely terrible for him and his family -- but if you are paying attention and looking at the road ahead of you, there is no situation where you accelerate for three full seconds into a concrete barrier at 70MPH -- not with Autopilot, and not without it.