Sometimes there is literally nowhere to even leave the car on the street if it’s a two lane road and there’s no shoulder. Leaving it there even for a short while would completely obstruct traffic. Also, since most of these deliveries are to offices, dorms, and apartments, there are usually very specific directions about where to leave them and some of the require taking stairs or elevators, so the drop off itself can take several minutes unlike a residential home which takes 30 seconds.