The reason is that each cable in its own package is a separate SKU, purchased from a separate supplier, and tossed one-per on an assembly line that is filling the box you finally received. I suspect that if, say, samsung or nintendo was told to stop putting bags on every single cable, they'd just add a step to their assembly line for snipping open the existing bags and tossing them in the garbage.
The real solution will be (as usual) more complex than you'd guess at first, and I don't have a good idea for where you'd start. Maybe find the point in the supply chain where these baggies are first introduced and add a tax on them at that point?
To be fair, that would still be an improvement because we could make them isolate those bags and recycle or burn for energy or something. It is by comparison impossible to control what consumers do with those bags.
The real solution will be (as usual) more complex than you'd guess at first, and I don't have a good idea for where you'd start. Maybe find the point in the supply chain where these baggies are first introduced and add a tax on them at that point?