It works out pretty well in theory. Even at minimum wage the cost of the driver is a lot of the cost of the taxi ride. It does all hinge on the cost of the vehicles + the cost of monitoring + the cost of maintenance being low enough to offset this though. Cost of vehicle is higher in the case of waymo but even 3x the cost is still useful, cost of monitoring is probably still a bit high at the moment but is the main thrust of improving the tech, and maintenance is not necessarily much worse than a normal taxi.