I mean… just gonna go out on a limb here and guess that the expression exists because within the history of every book ever released, there would be some fantastic books with absolute stinkin’ covers.
Yes, covers are there to help you judge a book. But if that was the only metric you used, you would miss out on some good reads.
This is less to do with single-use plastics, but plastic is often a really good option from a functional POV. It doesn’t conduct heat like metal, it doesn’t break like glass/ceramics and has better moisture resistance than timber. (Not saying plastic couldn’t be replaced a lot of the time, but some times it’s a frustratingly good option).
In terms of complete single-use plastic replacement, I’m not sure, but would also be interested. I’d hope it’s mostly possible.