Maybe we shouldn't put the whole burden of world justice on Waymo, this allowing it a complete invasion of the privacy of both the people who use it and those who don't? Guy takes a drugged up girl on the train, should we hold the train responsible for the outcome also?
Public trains are covered in camera surveillance and that footage is very often used in conjunction with tracking down and prosecuting criminals. You should have no expectation of privacy on a public train.
I think the risks are different on a train, which is far more public than the inside of a taxi. There are more likely to be other people and/or an operator to intervene.
Are you aware of BART Police or MTA Police? All trains have conductors who monitor passenger behavior and enforce rules/laws.