Even when just looking at marginal costs, I doubt Waymo is half that of a human driven vehicle. If we assume a robotaxi lasts 200k miles before being retired, then the cost of the vehicle alone ($75k) is 37.5 cents per mile. If a vehicle drives 200 miles a day, that's $5 of electricity (250Wh/mile x 10 cents/kWh), maybe $15 of labor to clean, and the space to park it near downtown ($3/day). That's another 12 cents per mile for a running total of 50 cents per mile. Then factor in maintenance (tires, brakes, suspension, etc) and you're probably close to $1/mile. Then you also need support staff, remote operators (approximately 1 per 50 vehicles, but paid significantly more than Uber drivers), and plenty of compute and storage for the high resolution maps (which must be constantly updated as the environment changes). And none of that includes the R&D costs to improve the vehicles or the self-driving software. Yes many of these costs decrease as fleet size increases, but it'll be a while before it gets below $1/mile. (Nationwide, Uber's rates are $1-2/mile depending on the area.)

There are other considerations as well. For example, available ride shares can scale up/down with demand, while Waymo & competitors will need lots of spare vehicles to satisfy peak demand.

I'm certain autonomous vehicles will eat up the market currently held by Uber/Lyft/Taxis. It's just going to take longer than a lot of people expect.

Those are some good points. Waymo & self-driving cars only makes sense in markets where the cost of paying a human driver is much higher than the amortized cost of operating a self-driving vehicle. As an extreme example, in Bangladesh a driver will work for ~$0.25/hour. Self-driving cars don't make economical sense there, the additional cost of making a vehicle self-driving never pays off vs having a dedicated driver.

Waymo can expand easily in markets like SF and NYC, where drivers are guaranteed a minimum pay rate of $22+ per hour, but will make less and less economic sense in cheaper labor markets.