It's not that simple. From what I understand, so much gil was able to be made from it that the popular RMT places were able to sell it for 15 bucks per million, which was like a 300% lowering in cost and the same rise in supply. Unchecked, it could have led to a reboot of the old COP exploit which lead to 10 million gil haubies. Prices on many items had been inflating recently, so they were right to worry, but they just overreacted by banning using automated tools.

The problem with FFXI is that the economic role of it has way too much impact on the game side of it. It's harder to make money than it is to level in the game.