I would say it's very clear as the international publisher that it is their job to market and increase awareness of products to people. Nintendo was that publisher, and they absolutely failed to do that post DQIX, where a number of people here - myself included - felt they were only releasing games outside of Japan to meet some sort of quota deal with Square-Enix. DQ VI and Monster Joker 2 were their last major DQ releases, and both were just sent out to die. No marketing, no awareness on those games beyond the hardcore fans who were already getting the games, and the franchise simply needs more than that. Those games probably failed to meet expectations - be it of Square's super high expectations or Nintendo's low ones - and that killed the series here for the most part. But marketing and awareness of those games was nowhere near it should have been, and those games tanked, Monsters Joker 2 rightfully so for Nintendo waiting years to bring the game and giving us the outdated version.
Piracy has always been an easy scapegoat to cite when games underperform as well. These are the same companies who in the last few years have essentially played that game with used titles, and while I am not doubting these have some impact, I am willing to bet it has less of an impact than the big companies say it is. It has some, but it's always expanded to make every download seem like a lost sale, and that's a topic not even worth getting into because of how absurd it is.