Those passengers would already have the car parked at their house, or the restaurant they were at. The Uber driver has to drive to pick them up. Then once they

Those passengers would already have the car parked at their house, or the restaurant they were at. The Uber driver has to drive to pick them up. Then once they drop them off, they have to drive to the next fare. Sometimes they even circle around high traffic areas in heavy traffic in order to get to customers faster. Basically anytime you see an uber driver without a passenger is likely extra car time on the road compared to what those passengers would have done with private cars.