Yep, plastics can be wildly incompatible. Growing up my dad had a fishing tackle store with bulk plastic fishing worms. Customers, being customers would occasionally pick them up and leave them at other places in the store, like in another bin of plastic worms or some other plastic object. If not noticed quickly this could lead to a big clump of plastic goo as they reacted and melted each other down.

Right, my point is that plastic items originally were meant to replace heavier/bulkier items, but with a comparable longevity. Not to be used as single-use throw-away items. The need to recycle comes from the fact plastic stopped being used for durability, and it hence thrown away in humongous quantities.