Because I have. Thousands of items. I would MUCH prefer someone to not pay for the item than for them to pay, me to ship it, and then they change their mind and return it. Because ebays policies are entirely pro-buyer, there’s a good chance you’re paying for shipping the item out and paying for shipping to have them return it to you, while they get a full refund.

Do you not return things to stores that you decide later that you don’t want? Are you not overly concerned about the expense the store incurs refunding you, restocking the item, finding a new buyer etc? Because not paying for your item on eBay accomplishes the exact same thing, but saves the seller shipping fees and allows them to relist the item immediately. Is it a great thing to do? No. Duh. But it’s better than buying something you don’t want and then returning it after it arrives.