Monster Hunter has been an extremely popular series in its home country of Japan. The titular action-adventure series are known for their extremely cooperative, and challenging gameplay. But, even though Monster Hunter continues to hit the top of the charts; the latest iteration in the series has actually sold less in the same time frame as previous versions.
Notice that it is still first in the charts, but that's not the point.
For reference, it's already been noted that Monster Hunter X sold comparatively poorly when faced with the other games. But, there was speculation that this was due to the lack of content from the game. Yet, with the release of Monster Hunter Double Cross and its sales, this is starting to seem rather doubtful. After all, Capcom is known to create new versions of the same game until it bleeds the series dry of mostly everything except the few diehard fans.
There is a reason that Capcom has the trope "Capcom Sequel Stagnation" named after them. Monster Hunter is no different, often seeing multiple releases of the same game, but with additional content. This has the unintended side-effect of causing sales to spike for a bit, but eventually exhaustion sets in and players all, but abandon the games they once loved. It's a harsh reality, but Capcom truly needs to change their marketing methods.
How long before Monster Hunter vanishes similar to Megaman, or their other big name series that have disappeared from the gaming radar for years? We'll eventually find out.
Do note that the first week sales for Monster Hunter 4 were 1.7 Million copies, compared to the 800,000 copies of Monster Hunter Double Cross