In some outdoor city markets such those in Asia, where pollution and dust is a big issue, retailers will often have one single clothing item on display and the rest in their original plastic wrap. This is how customers prefer to buy them as they are assured of a clean garment and retailers do not mind as labour costs are not high. However in first world department stores and boutiques, retailers will have all the garments out to encourage customer interaction with the products, as well as promote self-service. When customers see items in bags, they immediately think back stock and off limits to their inspection.
DON'T: Yes, this is the top shelf but these specific merchandise are not displayed elsewhere and I wanted to take a closer look at the gray sweater. However with the plastic cover, my impression is that these items aren't for sale. Oh well, possible lost sale!