Retailers tend to order more merchandise than they need, a typical example of this practice is when they buy seasonal stock. That is why retailers work with merchandise liquidators to sell off their customer returns at reduced prices.
Since most stores do not sell second-hand products, those products just sit in their warehouses. That is because those products can no longer be classified as brand new and need to be labeled as second-hand goods. Whatever the reason may be, many retailers will have volumes of stock that sit in storage that cannot be resold in their stores.
Customers return items to retailers all the time for various reasons: maybe they changed their minds perhaps the product had a slight defect or imperfection, or maybe it did not work as intended.