[notahacker]

To be allowed on regular public roads without humans behind the wheel in most jurisdictions, they're going to have to be better than people in virtually all conceivable circumstances rather than just on average. (This isn't even necessarily a bias in favour of the status quo or irrational fear of machines though those exist too; the analogy would be a person with unusually quick reaction times who drives 100k miles every year without incident still being liable to lose their licence if they're proven to have a bug in their system that makes them occasionally inclined to drive under the influence or faster than speed limits...)

[ghaff]

And, as a practical matter, not to fail in ways that average people (aka the voters) won't see as crazy and incompetent--even if the occasional tired or under the influence human driver might have done something equally bad.