They offer free shipping to your home.
Sometimes stores offer free shipping when they're out of stock in a size or low on inventory of a particular item, which is not uncommon during the busy holiday season, but this is often just to get you to make the purchase that day. You may be better off shopping around and finding a better deal with a competitor.
Plus, you could end up waiting seven to 10 business days for your purchase, and by that time, you may have reconsidered how much you actually need it, or your gift deadline may have passed.
Source: US News and World Report