Because you can never have enough bags, but you can certainly have enough G20.
True story: The other day I’m at the pharmacy waiting in line, while the lady in front of me pays for a greeting card. This woman asks the cashier for a bag. The cashier gives the stock-Toronto response, “That’ll be five cents, please.”
(Yeah, you got me. She didn’t actually say “please.” Please isn’t really part of any stock-Toronto vernacular, but that’s another story.)