This is likely done to try and reduce everyone pilling onto one DC like they are currently and get some people back to their native DC. ATM loads of people from Chaos are pilling onto Light as it has the better organised raid scene. The same thing is happening in America (with Aether I believe) and Japan. It looks like they have specifically chosen different DC's from the popular ones to be the ranked PVP servers - so if people want to do it they will have to travel and thus ease congestion on Light, Aether etc.
