It's not like Waymo/Uber can roll in with autonomous taxis in every city just because Uber figured out the local regulation - many cities would have explicit regulation for anything driverless. I think it's the later point - they want to stay in the shadows until they are super confident. I wonder what will happen to Uber eventually though.

It'll be interesting if Cruise ends up partnering with/acquiring Lyft. Although Cruise seem to be still betting on their Origin vehicle.