*Cats and dogs sometimes eat plastic bags because they are attracted to the scent of beef tallow, a type of animal fat often used as a slip agent in the manufacturing process of plastic bags, which can be appealing to their sense of smell, making them lick or chew on the plastic.
*Paragraph 8 from this article - https://www.petplace.com/article/cats/pet-behavior-training/plastic-bags-and-cats-a-love-affair
Animal Fat
Most plastic bags are made with slip agents to reduce the friction in the material; these slip agents are often made of beef tallow. Tallow is very nutrient dense because it contains conjugated linoleic acid, antioxidants, fat-soluble vitamins, and omega-3 fatty acids. If you’re wondering what tallow is, the Ultimate Paleo Guide provides an excellent comparison. “Pork is to lard as beef is to tallow.” So your cat may be licking your plastic bags for that yummy beef fat.
I looked this behavior up a few years ago, as one of our 4 cats, our 14 lb black-and-brown tabby guy, absolutely LOVES plastic grocery bags. If there is one in the house, he shows up immediately He usually chews the handles off it we don't catch him at it right away.