Because there's no option to give someone 0 stars. It's 1, 2, 3, 4, or 5. I don't use Uber much; I'm mostly a Lyft person, so I'm not 100% sure how Uber does t

Because there's no option to give someone 0 stars. It's 1, 2, 3, 4, or 5. I don't use Uber much; I'm mostly a Lyft person, so I'm not 100% sure how Uber does things, but here's how Lyft does it: if you open the app within 24 hours of riding with someone, it opens the rating screen, and you have to rate them in order to proceed. One star is the lowest you can rate somebody. If you want to proceed without rating them, you have to wait 24 hours before using the Lyft app. If you do, the screen goes away. It used to be that if you did this, their rating wouldn't be impacted at all; as far as the rating system is concerned, you never rode with them. But a few months ago, they changed it so that waiting 24 hours without rating someone will automatically rate them 5 stars. So if you try to give them no stars, all you'll end up doing is giving them 5 stars. Again, I'm not sure exactly how Uber does it. I don't remember if it has the 24-hour window or if you just can't proceed at all if you never rate someone, and if it does have the 24-hour window, I don't know what happens when the window expires.