We anticipate that even with this update, third parties will continue

[Azuri]

Doesn't RMT pay full price for codes?

I understand they discount the codes to get people to their sites and buy more than the items they're advertising from Mogstation but I fail to see how SE loses money form those initial sales. If anything it only reduces the sales from the honest people who can't gift their friends now. So how will it hinder RMT? I only see SE losing sales to RMT and now to the community as a whole.

Someone please explain how this saves SE money and the reasoning behind it?

RMT vendors buy those codes with stolen credit cards. When the actual card owner issues a (rightful) chargeback SE is forced to return the money and gets hit by a big fee from VISA/Mastercard. As a general rule, chargebacks are extremely expensive and detrimental to the vendor.