Yep, otherwise they don't work. Cardstocks don't hold milk, sterile. Pure aluminum cans dissolve into food contents. Glass lids can't seal tight enough.

Food producers and public health authorites has food poisoning lawsuit and human safety at higher priorities than environmentalism. So they just make it all packaged up in plastics.

Doesn't mean some sort of waterproof inner wall coatings can't be made in the future, though. Maybe if we substitute PE with engineered PLA made from agri wastes and made sure to burn it, that could make sense someday.