Biodegradable plastics tech is tough. It’s going to be variable between a year and 100 years, and also cheaper than petroleum based tech.
I think we’ll get there. In the scheme of things, it’s early days for this kind of stuff.
Now, I learned an interesting detail (assuming my source is correct) the other day: The “Great Pacific Garbage Patch” is made up of ~50% discarded fishing nets. This is low hanging fruit!