Because plastic is not and has never been recyclable. Plastic “recycling” was invented by plastic manufacturers to shift blame away from the producer onto the consumer.

When you do sort your plastic for recycling you’re causing more harm than good because it gets shipped around as people pretend it’s recyclable. Eventually ending up in east Asia where most of it ends up in the rivers and eventually oceans. It would be far better to put your plastic in a landfill.