Nintendo publising Dragon Quest IX outside Japan

Nintendo has announced that they will parter up with Square Enix to release Dragon Quest IX: Sentinels of the Starry Skies this Summer in North America and Europe.

Dragon Quest IX: Sentinels of the Starry Skies has sold more than 4.15 million copies in Japan since its release back in July 2009. However, outside Japan the series aren't really a success. Is this the reason why they don't release the game themselves?