Like the post title says, I'd like us to pull an answer out of SE.

Why on Earth would you put JP, a small (although populated) island, on its own datacenter, and NOT put Europe and North America, which are MASSIVE (AND populated), on their own datacenters?

The reason the Japan servers are stable is because they have a whole datacenter to themselves. Why are us North American players not on our own datacenter, and Europe on their own, to alleviate the stress?

This is a glaring design flaw, and I'd like to hear the actual reasoning behind it. It seems like most of these load issues could be avoided if that simple step had been taken.