Simply? The driver never signed up for those rides in the first place.
Imagine being pitched an engineer job at an engineer salary with company later expanding into haircutting business and ducking your bonus for not generating enough haircuts.
I've never been an Uber driver, but as far as I can tell from my conversations, they do indeed sign up.
My app sometimes says there are no Uber X available in my area, but 5 or 6 Uber Black. How could that be possible unless the Black were not automatically signed up for X?
Imagine being pitched an engineer job at an engineer salary with company later expanding into haircutting business and ducking your bonus for not generating enough haircuts.