As a Japanese player myself playing from NA, I can tell you this little bit. In Japan, gaming is not as "wide-spread" or as glorious as it is here. I don't mean to say that the nation hates games and fun. It's just that the notion of gaming in Japan is different than it is here. In Japan, the most widely adopted form of "gaming" is what we would probably best refer to as "arcade style games." Taiko machines, Beatmania consoles, stuff like that. The era of PC gaming has not really reached Japan as much as it is spread in NA/EU.

The population in Japan vs. NA/EU that are playing FFXIV: ARR, proportionally speaking, are probably quite a bit lower in Japan than it is in NA and EU. I really don't see why NA/EU has fewer servers than the Asian region.