[KozmoNau7]

They do it because convenience sells and because marketing has indoctrinated us to constantly desire Fresh! New! Pristine! Shiny! products.

Using plastic is the cheapest way for them to do it, since they don't care about the externalities and don't have to pay for the long-term damage they cause.

The solution is regulation. Make the manufacturers bear the costs of responsibly handling every bit of waste they produce, every bit of plastic. Make them responsible for taking back their waste, perhaps with a deposit system like on empty bottles. This will make them reduce their use of plastic packaging, in favor of better designed and actually biodegradable/reusable packaging.

And follow up hard to make sure they actually meet their promises, and don't just ship it all to a third-world country, because they will do that, given the chance.