With a car, you should always drive at a speed so you can stop in the distance you can see and predict as the driver. With a train, you can’t really do that if you don’t want to go walking speed around every bend in the track. So a high speed train is always operating in a state where it needs external sources to tell it if the way is clear.

Perhaps part of the answer is liability.

Also because nobody feels profitable to use Waymo to seed chaos and create riots. In that case the situation will change drastically in a couple minutes.

People would still blame Waymo, not the government, so there is not any gain unless you are a Waymo's competitor.