> imagine if all packaging was compostable, you could just throw it on a pile in your back yard and it would turn into fertile soil within a couple of months

Nope, this is emphatically not how the compostable materials you're talking about work. I invite you to try it: you will not see much degradation of the object even after a year, even with shredding and in a well-maintained pile.

Almost all of these materials need special composting processing; one of the key requirements is adding quite a bit of heat. I've known several restaurants/groceries trying to use compostable cups/utensils/etc. whose compost service eventually required the pickup to be completely free of these items. Portland, OR has municipal compost; they likewise cannot process these items: https://www.portlandoregon.gov/sustainabilityatwork/article/...

These materials may be better than "traditional" plastic, but the "compostable" nature is rather oversold. They still need to be handled in a very specific manner. They won't break down without quite a bit of help.