Isn't plastic basically a byproduct of oil production? I'm not super familiar with the market, but my understanding was that gasoline was the main drivers of drilling, not the market for plastic.

It seems to me that recycling would just drop the price of plastic and encourage use elsewhere, but burying it underground would remove the byproduct.

Every petroleum product was a waste product at some point until they discovered a use for it. If no one used oil for anything but gasoline, I expect drillers would pump the distillation remains back down into old wells.

Petroleum cracking happens very long distances from the actual oil wells. I have never heard of this happening.

Because there is no waste...