I am with you OP. I really avoid taking the whole family to the shops, it's hell for all concerned. Either I go alone or DH goes. He takes a list of what to buy, it's not rocket science. Or if we are popping back from somewhere one of us will wait in the car with the kids and listen to music.
I do sometimes take them shopping during the school holidays but I much prefer not too or will online shop. I do find it weird to see whole families shopping together Saturday afternoon when the shop is rammed, everyone looking stressed, but I guess each to their own. It doesn't bother me at all, I just don't understand it.
I do occasionally take 11yr old DD shopping with me so that she can choose her own clothes and also to practice her shopping skills (no, they really don't need to learn it at 5, they honestly can pick it up quite well later on!)
Also weird to me is if you go to large shopping malls at the weekend and see whole big families there, obviously making a day of it. I can't think of anything worse but then I don't really enjoy shopping that much! I'd rather go to a park or the cinema with them.
The oddest one was during the last half term hols, I popped into a kids shoe shop with the DCs to get DS some shoes for school. However there was a whole family in there choosing shoes for two young children. Mum, dad, grandparents, and also another couple who were with them (never quite worked out who they were). So yes 6 adults. Lots of shoes being tried on, everyone having an opinion. Their kids were getting fed up. After waiting a while and my own DCs getting restless I gave up and went home! It bemused me. Maybe it was their idea of a family outing?
But as others have said, everyone is different, I am not judging, just never understand it.