Also, some drivers are lazy and don't get proper mounts for their phones. I've had a few Lyft drivers spend much of the ride with their faces buried in their phones because they didn't bother to get a mount and don't want their nav to speak out loud.
I also had one reckless idiot spend the whole ride texting while driving, too.
I've seen drivers parked in lots when they are awaiting a request but in places where parking is charged such as downtown, I think they prefer to keep looping around blocks.
There may be an interesting case study to be made on the environmental impact of these idling cars.