Actually, you make a really valid point, but it's leading me to an unfortunate conclusion.

If bacteria was developed that could break down plastics and did actually break free to start digesting plastic in the wild, that would really clean up the earth, for maybe 10 years. But then the manufacturers would start using "more durable" materials, they'd slightly change their plastic chemistry to resist these microbes and we'll be in the same boat we're in now, where plastics don't break down.

Because the thing is, one of our primary uses for plastic is when we want a material that won't rot or rust, so breaking down defeats is purpose. We want plastic to not break down, so our products continue to work longer. But we also want plastic to break down, to not pollute our environment. These two goals are completely at odds with each other. The result is, and I now 100% believe this, we will never really have bacteria that breaks down plastic, long lasting plastic waste is a product of our own desire for "quality" products.

That would be really cool if so. Except for Blahaj. Don't eat Blahaj. >:(

Wood is a biological material made from molecules that have been sitting in Earth's biosphere for hundreds of millions of years:

Wood
→ cellulose
→ hemicellulose
→ lignin
→ sugars/aromatic compounds
→ microbial metabolism

Those molecules contain lots of chemically accessible bonds, especially C–O bonds. Plants built them using biological chemistry, so other biological chemistry can, in principle, take them apart.

An enzyme isn't a tiny animal chewing through plastic. It has to contact a polymer chain, bind it in an active site, chemically cleave a bond, release the products, and repeat.

A plastic can thwart that by being:
hydrophobic + highly crystalline + insoluble + chemically repetitive + physically inaccessible.

There's no evolutionary law saying organisms must eventually become capable of rapidly consuming any energetically favorable substance.

Evolution has to find a chemically feasible pathway. And even if it does, decomposition might be:

plastic bottle → 150 years

rather than

plastic bottle → three weeks.

And amusingly, we could simply change the plastic. If PET suddenly became unsuitable for decades-long applications because PET-eating microbes became ubiquitous, we'd manufacture polymers resistant to those enzymes, add protective layers, alter crystallinity, or use different polymers.

All and all, I’m doubtful microbes will come to our rescue. Unless we engineer them for the task, that is.