NYC people uses it because the alternatives are either slower or much more expensive. I'm sure they'd rather use a waymo if it was as fast and cheap as the subway.
That's the whole problem. Car transportation simply doesn't scale, so there will never be an option to use waymo that's as fast and cheap as the subway. It's worth calling out that an efficient train system is vital to keeping car traffic moving quickly, because once everyone is in a car, it's gridlock.