The thing is, it's not PayPal's money that's being refunded to people - it's the sellers' ill-gotten gains, so why should PayPal try to wriggle out of it? By making it harder for people to be refunded for the purchase of fake goods, they are guilty of aiding and abetting these criminals.
Using PayPal to receive payment for counterfeit goods is in fact against the terms of your PayPal agreement, so why don't they ban these sellers?
Since PayPal is owned by Ebay, you would think that multiple claims for fake goods would trigger a report to Ebay, and the ebay account would be closed (as well as the PayPal one)