Maybe the refrigeration in the trucks only stays on if the truck is running? I can certainly understand why they're not driving around the block 10 times and nearest available legal parking spot is likely very far away.
I used to get FreshDirect when I lived in Astoria. I didn't have a car at the time, and my landlord told me not to drink the water from the tap. Gallons of water were too heavy to carry home (more than 1 at a time), so I would have several delivered, along with my groceries from the week. Groceries are heavy, and especially in JH, the supermarkets are far from most of the residential areas. If someone is older, has children with them, or injured or disabled, it can be difficult to carry what they need home without making several trips over the course of a week.
FreshDirect has been sending me promotions lately... 15% off my entire purchase to come back, and the emails come once or twice a week. I consider it, but I hate that you have to pick a "window" of time for delivery and then wait around for them. If I didn't have a car, I certainly would, though.