The reason races of FFXI were used was what I've quoted on Tanaka,
http://www.ffxivcore.com/topic/21505...aka-interview/
That's all, he wanted to draw the player base from FFXI into FFXIV. And it was a horrible decision in my opinion because it made players believe this would have been a sequel.
Additionally, it served no purpose in design to reuse these races in a new environment. The races for FFXI were crafted with the design of the nations, they were molded to fit the story and plot. Humes, elvaan, and tarus had a nation, mithras were mostly migrated over and formed communities within forest-like locations such as Windurst and Khazham, galka lost their homeland and reside with humes. They had culture and history relating in the development of their nation and beliefs. And when yanked out, and slapped into FFXIV they are nothing but another anonymous dude in game.
The races of Ivalice, however, only appears only in "Ivalice Universe" based FF games for a reason. They are all residing in the same world, they are part of the elements that creates the cultures and society of the world Ivalice. They exhibit the same behaviors and social standards. You also see the same characters such as Vaan, Balthier, and Fran making guest appearances in some of the FF spin off games. It flows in the same game timeline. It is all part of conscience design, and not just a mere gimmick to draw players in from another FF series. It is not branding for the entire FF series, it is to hold continuity for the Ivalice Universe.