Grocery bags are disposable plastic. In my state they cost a few cents each as of a couple of years ago. Reusable bags are common, but it's also common to forget them and need to buy disposable bags. Most people reuse them as e.g. trash bags for bathrooms.

the us largely does not charge for bags directly, they are a consumable that is part of the store's customer overhead. At cost each bag is around 3 cents, and probably holds 15 to 50 dollars of merchandise that is being sold at around 2% net profit generally.

people often keep the bags and use them for other stuff, like trash bags or plastic linings or makeshift gloves. not everyone does. it's wasteful, yes, though on net carbon impact it's probably lower than plastic reusable bags and many plant fabric ones given a plastic industry exists anyway.

Ah so your state is just being annoying. They're 5 cents in OR, paper or plastic.