It being far less expensive, seems to be the standout reason. Normal people can't afford $700/month for food delivery services.
So I'd be looking at about 4x the cost if I ate a delivery pizza every day.
How do the figures compare in your area? Is delivery food radically cheaper?
A couple of footnotes: 1. Pizza is absurdly cheap, even for takeout food. I don't really understand how that works. 2. I prefer takeout over paying for delivery, which saves a lot. My favorite pizza places are in walking distance.