To be fair, humans are fairly poor drivers and generally can't be trusted to drive millions of miles safely.

Actually humans are fairly good drivers. The average US driver goes almost 2 million miles between causing injury collisions. Take the drunks and drug users out and the numbers for humans look even better.

I don't think averages work that way

Incorrect. Humans are fairly good engineers, so cars are pretty safe nowadays.

If you include minor fender-benders and unreported incidents, estimates drop to around 100,000–200,000 miles between any collision event.

This is cataclysmically bad for a designed system, which is why targets are super-human, not human.