"it's too hard" should never be an excuse to break the law
It's also a lot different with a permanent installation that is verified once than this kind of tragedy-of-the-commons temporary minor abuse of public space.
But either way, it is the responsibility of the regulatory body to enforce. As other people have noted, this is not a Waymo problem, they're just following the status quo.
Exactly the case with the ADA. Since GOOGL is responsible for Waymo behavior, they will be liable in a class action suit where they willfully violated the law, putting others in danger, in selling their product.
There is not any way around it. You can avoid this issue like Lyft does, by having divers make that decision and by them being not worth suing, but GOOGL is worth suing, and you can’t intentionally violate the law and put folks in danger without it giving you massive amounts of liability.