More money. The game only rewards the top players for various events. So if you want new players to come, they're not going to join a server that's already way ahead of them. No amount of money is going to get you to catch up in levels.

So a new server is the best way for a new player to start out. Each server ends up being a tiny community of people and each one has people cash shopping their way to power to be number one. If it was just a single giant server there would be no incentive to spend money because some rich guy will outspend you every time.