Silkroad has a lot of players. As already fyfly said, upgrading an existing server costs much money.
By making new servers, it will come to one point when all players that are sick of lag on Xian, Aege and some of "older" servers will go to new and so laging is going to stop. Since Silkroad is still in development it needs time to become one of the biggest MMORPG on the net

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