AFAIK cellulose, for food packaging, is only available as a clear film and not as a firm rigid plastic. I also don’t think cellulose can be recycled so the end of life is either landfill or composting.

It’s also not as functional as OPP films, that is what most of the thin clear sealed plastic packs are made from and also the windows in some packaging. This is being addressed though with products such as Natureflex film which has a cellulose core and moisture barrier coatings on both sides. These barrier coatings themselves are a form of PVC which although not compostable is in an amount which allows the film to pass current certification for composting. This does have a limitation though as it affects the bags ability to be perforated, which many of the OPP bags are.

Natureflex is also, currently, a lot more expensive than OPP so where so much is price driven there isn’t the willingness to do this.

There is a lot of product development going on in packaging and as with most industries quite a few seemingly great ideas are not practical on a large scale.