I suspect that Waymo car's could operate in a lot more areas than they do. The issue is that Waymo are trying to sell the service of safe travel and not a car with an addon you can pay for which doesn't actually work.

In other words, since they accept liability for their cars it's not in their interest to roll out the service too fast. It makes more sense to do it slow and steady.

It's not really a strong argument that their technology is incapable of working in general areas.