

Whilst paper and canvas is biodegradable, plastic as a material has certain useful traits compared to paper and canvas, hence why making/developing similar biologically based and degradable materials helps reduce our reliance on it.
Examples of such traits: Liquid resistance, non-permeable to water, see-through.
Probably that it’s based on corn-waste. Most I’ve seen are sugar-cane based. US grows a lot more corn than sugar cane.