Waymo needs ridiculously detailed maps before it can operate somewhere, so its expansion is necessarily slow, along with the legal impediments they face but they're expanding. Phoenix and San Francisco, and now LA and soon Austin. If no one else has the technology to do it as well as they do, that's a pretty strong moat. No one else has access to the same resources they do. Which, since they're owned by Google, we can assume Google is helping them a lot. Unfortunately Waymo
can't ship a simpler intermediary because they refuse to do it, because that kills people. A self-driving car that works right up until the moment it disengages and you get into a car crash that kills you isn't a product they want to sell, unlike others in the market.
They have a product and it works and a lucky few can use it right now. Unlike other products, they can't just spin up a factory and make 10 million more and just sell them world wide like you can with an iPhone. They're undoubtedly working on a new vehicle platform that won't have a steering wheel or driver's seat.