I work for a supermarket and we get occasional complaints from customers when delivery drivers won't bring their shopping up to their flat, however our online shopping T&C does basically say that whilst we will deliver to the main door of your building, if you're in flat our divers are allowed to use their discretion as to whether they'll bring it right to your front door.
Delivery drivers have many different orders to fulfil, they have to lug crates of (often) heavy and/or bulky items up and down stairs on a daily basis and they have to prioritise their health and safety over individual customers' wishes.
A lot of the time they will do their best to go beyond dropping the stuff at the door and leaving, but when you have an order of: a 20L bag of cat litter, crate of 20 tins of cat food, box of 30cans of coke, 6 pack of bottled water and all the other bags of shopping, it's not like they can just tuck it under their arm and hop up the three flights of stairs to your flat.
Then factor in the fact that grocery delivery routes often try to group orders geographically and, in my town at least, certain areas tend to be all flats ... so your delivery driver may have already carried half a dozen orders up 10 flights of stairs today and yours is just the delivery that broke the camels back, and if you have no reason not to help, then you should to make their job easier, especially when they are using their discretion to even deliver to your front door.
One of my colleagues ended up off work for over 6 months because they hurt their back lugging heavy shopping crates up and down stairs to customers. When they came back they were ruled fit for work but doctors put a limit to the weight they could carry at once and the maximum flights of stairs they could carry stuff up before they risked re-damaging their back. They were instructed by managers to stick to our "deliver to the main door of your building" rule, unless there was a lift, no matter what customers said (and of they did use their discretion to ignore that instruction they acknowledged it voided their insurance cover). The store would rather deal with customers being unhappy - as they technically had agreed to the T&Cs re:delivery point and the fact it was driver discretion as to if they brought it further - than all the issues that arise from workplace injuries.