You can take this in the other sens too. Lots of people would want the goods just for the in game item. But paying 35$-40$ and more for an in game item doesn't feel attractive, even though this price is for the goods. So they don't buy it.
Now, if you put only the in game item in the mog kiosk, for the same price or a bit higher than the other item from the same category, all those people would be more inclined to buy it, which at the end would represent a lot, taking into account that new people will be able to buy it too. It's a permanent gain that at some point will be higher than what the goods actually fetched for the game, considering that the good also have production costs, and sending costs.