In this specific case, because if a driver is watching the road in front of them, four seconds is an awful lot of time to watch yourself head toward and then accelerate into a cement barrier, all without touching the brakes. It's fine to want Autopilot to be better, but as a matter of law, it is the driver's responsibility to slam on the brakes in that situation, and move into a legal lane.
More broadly, it's because the contract of an L2 system is that a human is in control at all times. L2 systems are assistive and not autonomous. They will never disobey a driver's presets, nor override a driver's real-time inputs, even if the car thinks it is safe(r) to do so. This is a major design principle behind every L2 system, and the reason why there are no scenarios where an L2 system is considered at fault by law.
Now obviously, if there were a bug that caused an L2 system to override a user's input -- say disregarding someone hitting the brakes, or overpowering the steering wheel, that'd be a systemic failure and grounds for a recall. But we haven't seen any cases of that, and there are hardware precautions (e.g. limited torque in the Autosteer servo) to minimize that possibility.
In this specific case, because if a driver is watching the road in front of them, four seconds is an awful lot of time to watch yourself head toward and then accelerate into a cement barrier, all without touching the brakes. It's fine to want Autopilot to be better, but as a matter of law, it is the driver's responsibility to slam on the brakes in that situation, and move into a legal lane.
More broadly, it's because the contract of an L2 system is that a human is in control at all times. L2 systems are assistive and not autonomous. They will never disobey a driver's presets, nor override a driver's real-time inputs, even if the car thinks it is safe(r) to do so. This is a major design principle behind every L2 system, and the reason why there are no scenarios where an L2 system is considered at fault by law.
Now obviously, if there were a bug that caused an L2 system to override a user's input -- say disregarding someone hitting the brakes, or overpowering the steering wheel, that'd be a systemic failure and grounds for a recall. But we haven't seen any cases of that, and there are hardware precautions (e.g. limited torque in the Autosteer servo) to minimize that possibility.