Because with a world 2, only one comes out with enough players to remain sustainable. If enough people hop on world 2 for the new economy bandwagon, it'll make people feel forced to switch if they want to play with the majority. The "world 2" will be the dominate and ultimately only server because of initial hype and not because it's what current players necessarily want, at the cost of making people who spend money on bonds being the real losers.