Uber drivers are already paid low wages and any price competition can lower their wages further.
Waymo has to pay for things that “come with” uber drivers: the cars, storage for the cars, employees to clean and maintain the cars, extra infrastructure to support the self driving cars like cellular data for each car, data centers, engineers, customer service to interact with police and resolve edge cases (will never go away). Waymo also has to pay all these people healthcare benefits and pay W2 payroll, not a thing for Uber.
Waymo is like a professional moving company competing on price with an army of lowest bidder independent contractors who already have a beat up graffiti van.
Highway is coming.
And scale will make it cheaper. It's only cheaper than Uber sometimes currently. That will change.