Cars don't drive in the dark. Roads are usually lit. And every car has its own lights for seeing where you are driving.
> Roads are usually lit
Not always. Definitely not all freeways.
> And every car has its own lights for seeing where you are driving
Not always far enough. Especially at freeway speeds on unlit freeways.
Interstate highways and local roads are generally unlit outside of urban areas. But in fairness, Waymos don't operate in those places anyway.