My guess is because there is a lot of fraudulent bidding on eBay.
A really good example of that was when they had one of the original cars from the "Dukes of Hazard" show signed by the cast up for bidding. The proceeds were to go to charity. The winning bid was over $2,000,000, and the bidder ended up not responding to the auction win notification--just someone bidding with no intention of actually buying it let alone have the money for it anyway.
We washed our hands of eBay when our account was hacked three times. Each time it was hacked, we had to set up a new account and password just to have it hacked again. Then, a purchase I made arrived damaged; and the seller didn't want to hear about it, trying to blame it on USPS. Although, she never bothered to package the boxed merchandise properly. She just taped a piece of paper with our address on it to the merchandise box (the thin kind of box) and sent it out unprotected. :nono: