Why are there pixies, etc. on the First but not the Source?

[YianKutku]

EDIT: Oops, I didn't see the new page, so my original post (that there are Moogles on the First) is redundant.

I admit to some curiosity that the Viera on the Source are mostly in Othard, while the Viis of the First are in Norvrandt, half the world away. Given they have lengthy lives and are also deeply insular (and thus not likely to migrate), I have to wonder if this is actually a decision made out-of-universe to allow for the newly-designed race to appear in the expansion, rather than actual lore.