Being helped by a man (or woman) when you are all dressed up may also be because they recognize that it would be bothersome to possibly get that outfit mussed or stained while digging in the nut and bolt bins, you know?
I've actually done exactly that at Home Depot, when I saw a lady dressed beautifully for a funeral who was there looking for small parts, to repair her suitcase trolley wheels before heading back to the airport to fly home.
If you are wearing high heels, schlepping heavy items can be dangerous. I think most people recognize that, and some would help with the lifting out of concern as much as chivalry. Courtesy in general is not dead, and it has jack all to do with the "morality" of women.