That's pretty typical, honestly. When working regular jobs, I've been paid one way, and not paid for time not working. The term is "waiting to engage", versus "engaged to wait". That is, if they want me to sit around to be available at a moment's notice, they pay me for that time. If I can go off and do other stuff and be vaguely available with whatever delay, then I don't get paid, because I'm not working and I'm not losing any of my own time.

I don't really think Uber should pay for time back directly, but they should definitely increase the cost of longer runs, especially to lower-volume areas where the driver might not have a fare in the other direction. (The driver is also not required to take any particular fare at all, so if they feel they'd lose money on it, they shouldn't take it.)

Honestly, you could make a strong argument that drivers are indeed independent contractors under US labor law. However, if the court has found that they should qualify for more pay and benefits, I'm certainly not going to argue that it should be taken away. In fact I'm going to celebrate it.