The worst part about plastic bottles is the energy required to make them.
They go through a 2 stage process where the plastic is melted and injection molded into a “pre-form”
Then they get fed into a blowmolding machine where they are heated in different areas by many 2k watt halogen bulbs. Once they’ve been heated properly they go into the blow mold where they are pressurized with ~500psi air.
The molds are liquid cooled through an industrial pipe system with an extremely large refrigeration system. The energy required to run all of the equipment is insane. A factory can consume as much energy in one hour as a standard home will in an entire year.
This doesn’t include all of the energy required for moving materials around since performs can be made at one factory and shipped to another and empty bottles are often shipped to warehouses and then off to the plant where they will be filled, then warehoused then distributed etc.