When it’s wrapped in plastic it can be individually picked. In a warehouse large quantities of stuff is stored away in bulk, sometimes palletized. A picker goes around and picks out the items from the larger bulk of items to put together a shipping order. If they were individually wrapped, whether by the warehouse or their distributor, it is for general protection(so that it feels new) and ease of handling.

Source: worked many of the lower positions at different warehouses for some years.