You could set up a payment system to buy items that's not a player account. You buy an item just to give. There's still a phishing incentive, but is it worse than any of the other content you can buy online?
Credit Card theft/fraud is why. If it was possible to "transfer" funds like this then mechanisms for fraudulent purchases will increase dramatically. Eve Online introduced purchasing in-game currencies because it was rife on the "black market" anyway and they also saw a huge number of fraudulent purchases and/or charge backs. 3rd party grey "broker" sites popped up with way below market rate prices, 99% of which are using fraudulent CCs to fund them, and bot accounts to transfer the in-game stuff.
