I guess for the anonymity of it all?
For instance it came in handy once when I sold a snowblower carburetor on eBay to a guy in Florida. He looked at the picture and thought it "looked" like the carb he needed for his lawnmower. Well low and behold, it was not the right carburetor...despite the fact that I clearly stated the model number and everything else he would need to know to make a knowledgeable decision on this auction.
So this guy, he decides to file a claim against me...saying the item was not as described. He wrote me several times wanting to return the item..BUT...he needed a return address. My auctions clearly state NO RETURNS. What does eBay do?? Not a god damned thing about it...so eventually this guy had to eat the cost for his dumbassed research and decision making skills. Why should I have to take the return and pay for shipping when I sold him what he bought?
Sorry for the rant...your question brought up a bad memory...