Can we blame Wii Music ????
"Several months ago we looked at the decline of the music game segment, and this month we revisit that area one last time. As the figure below shows, sales of music games have dropped by more than a factor of five since 2008. While the figures above are only for the January – October period, we can at least give full-year figures for 2008 and 2009. The total haul for music games in 2008 was over $1.6 billion. That dropped to over $870 million in 2009. Short of a Christmas miracle, music games won't break $400 million for all of 2010." - Gamasutra analyst Matt Matthews