It’s partially because of cost, new plastic is cheaper than trying to recover old. But very few plastics can be truly recycled chemically, much being reformed for other purposes. Glass and metals were always a better environmental choice (with their own limitations too), but plastic is so cheap and versatile it’s hard to compete. Not just plastics - just a look around the household imagining the lack of petroleum products, it’s amazing how it’s everywhere. Yet another dead end we’ve gotten ourselves into.