Plastic was a new amazing invention. Used alot during the war. War ends so now there is a massive surplus. Companies advertise it as a new miracle product. Won't shatter, can be reused countless times, super easy to shape and produce, easy to color, and super abundant.
Plastic companies then want to increase profit. It's not profitable if your product can be endlessly reused. Convince people it's single use and to throw it away. Cause massive pollution issues. Realize plastic's reputation has gotten too bad and might be bad for business. Make a sudden pivot and pretend that plastic can be easily recycled. Make advertisements telling the population pollution is their fault due to throwing away plastic and their responsibility.
Recycling doesn't need to work, it just needs to look like it does. Haters will shut up and leave them alone.
Recycled plastic also happens to be less durable and significantly more expensive than virgin plastic.