Plastic is air and water tight. It keeps the confectionary as you call it from getting moldy, stale and/or overly moist for a longer time. Basically plastic extends shelf life.
Why is the confectionery that is sold in movie theatres packaged in plastic which makes the loudest & most irritating noise to other people?
To keep the fine mist of popcorn butter from saturating it? To distinguish it from other versions of itself? Because it's in a box?