…why this is not a standard business model. Seriously, players will pay you to play your game and then pay you more not to play (portions of) your game.
Counter-thought: the majority of your game has not endorsed RMT. You only need a small minority to support a nigh-endless stream of sales. With 0.1% of the planet playing WoW, you only need about 0.001% of the planet wanting to buy gold to have more than enough customers. How much of your playerbase do you lose by endorsing RMT? Noted effects of “we sell gold” servers and “no RMT” servers? I imagine that, oddly enough, people will play on no-RMT servers and still want to buy gold, despite that being a legal option on the server next door.