[jltsiren]

There is a simpler explanation: every Waymo vehicle is effectively the same. If one makes a mistake, every vehicle will likely keep making the same mistake over and over again, until it's fixed. If the mistake causes harm, there is often a clear causal link from a flaw in the system to the harm, which can be a pretty good incentive to fix it.

Human drivers are all different. They also learn from their mistakes and change unpredictably over time. Humans can get away with all kinds of unsafe behavior, because bad outcomes are unlikely in any particular situation. If something bad happens, it could easily be a one-off issue. And even with systemic issues, it's easier to change the environment / regulations / vehicles than the drivers.