Anecdotally the vast majority of street blockages I've observed are from trucks unloading, illegally double parked blocking a lane of traffic, rather than for hire cars.
But as a bicyclist it's deadly. I'm in SF, it happens all the time on second St and on market. I thought they weren't even allowed to drop off on market but it happens all the time. It happens to me like once every 3 months but I see it every week happening to others. I keep an eye out for those Uber badges and expect to get cut off.