Drivers are just temporary anyway. Uber is going to be the company to beat when autonomous cars make Autos as a Service a huge business. I see that, and not some low-margin package delivery service, as the driver of their future growth.
Uber is a bad investment.
And it just so happens that Google has a large stake invested in Uber.
Uber has massive consumer mindshare, and its still growing fast. When they start phasing-in self driving cars you will have a day where your UberPool ride to work was driven by a human, but your UberPool home happened to be an autonomous car.
Uber is building a brand as the go-to transportation service and that won't be displaced just because another company deploys a fleet of autonomous cars with their own app. Even if that company is Google. Sure, it's a competitive threat, and I have no idea if Uber will be a brand people know in 25 years. But in 5-10? I think they are positioning themselves for dominance as the provider of autonomous transportation.