If the bag is very light weight then they are saving money by putting it into a box to protect the bag. Most of the time there is a season packet in the box also so you need to keep that with the stuffing. And a box has better shelf presence than a bag.
Surely it stops the package being ripped or damaged? I think there are far too many instances where companies overuse packaging, although I kind of see the sense in this one. It also gives more space for things such as directions, ingredients and so on.
Packaging serves a dual purpose: protection of contents, and effective display. Stuffing must be in either an airtight canister or bag to stay fresh. Bags do not offer protection from puncture and crushing, nor are they practical for grocery shelves. Canisters are more expensive to make and take up more space in shipping cartons. A good alternative would be a free-standing flat bottom foil bag like those used for salad croutons.