Copying: When the last lead vehicle changed lanes—3 to 4 seconds before the crash—revealing the fire truck on the path of the Tesla, the system was unable to immediately detect the hazard and accelerated the Tesla toward the stationary truck. By the time the system detected the stationary vehicle and gave the driver a collision warning—0.49 second before impact —the collision was imminent and the warning was too late, particularly for an inattentive driver. The AEB system did not activate. Had the driver been attending to the driving task, he could have taken evasive action to avoid or mitigate the collision.
So there you have it: "particularly for an inattentive driver".
Not really an expert in the field, but I think a major problem with self-driving in general is handing over from an autopilot to a human. This is something that cannot be easily solved just by throwing smarter technology at the problem. Even if autopilot technology manages to be reliable 99.9% of the time, this won't be good enough, because people will invariably think they can rely on it 100% of the time and fall asleep or get distracted. So this 0.1% can be potentially catastrophic, because you cannot go from being asleep to full alertness in 0.5 seconds. Besides, even if one actually wants to maintain alertness, it may be harder to be alert and not doing anything than being alert and doing something (driving).
So, unless autopilots can really really handle anything thrown at them, this will be a real issue. Although there is much willingness for people to convince others and be convinced that this kind of autopilot is very close to being a reality, I suspect it may be not.