some of them have collection boxes standing around, which only get emptied once a week or even less regularly. but yes, there is probably some like you described too.

When I did shipping and receiving we did exactly that. We'd make bales of cardboard in our baleing machine and stack the bales in shipping container and sent it back. They paid the store like $20 bucks per bale.

Where I lived at the time all shipping containers came in and went out on the barge so filling them up vs having them empty was a negligible cost difference according to the shipping company.