Paper bags are way more expensive than plastic
Many stores actually preach asking “plastic or paper” instead of the traditional “paper or plastic” in order to save a few pennies.
People don't really need bags
You have two perfectly good bags on the ends of your arms. They're called hands, and they are evolutionarily suited to carry things.
Proper bagging is an art form
Use boxy items to build walls inside the perimeter of the bag, next comes the heavy stuff, then top it off with lighter items. It's like Tetris. But with Doritos and butter.
Some people aren't capable of loading grocery bags into their car...
... but most just want someone to talk to, which is why they ask for help.
Wrangling shopping carts is actually great
Even in the summer heat, it beats asking people if they've found everything alright for the millionth time. Also, you can totally nap in your car.