1. Humans aren't gonna trust SDCs easily. The way I look at it, SDCs would be used only to transport freight for a few years before people can trust it enough for ride sharing. I personally believe that companies should focus on self-driving trucking rather than self-driving cars and pivot into ride sharing after a few years of successful freight transport. People would trust the leader in the self-driving truck industry more than a top-notch but unproven tech company. Let alone cars, as simple as elevators in the buildings were operated by actual people before becoming completely autonomous.
2. Uber is not just in the USA. SDCs aren't gonna be approved everywhere, even after it becomes legal in the USA. Uber still has access to that market, but Waymo magically can't.
3. Uber has other verticals too (Uber Eats).