Could be a data-based decision... and you might not like what will follow.

I can't talk about Square Enix or FFXIV but from my personal experience with another publisher and others MMOs (Again don't shoot me, this is not MY POV, just something I have seen in another company). For those games I worked on, after marketing studies, Spanish-speaking and Brazilian-speaking countries were put into the "low spenders" tier. Which means less promotion in these countries, less support and in some cases low/no localization.

Not saying this is the case for SE but it is possible that decision are not taken by "how many people speak this language" but more "how many spenders are in this region compared to others".