Actually, I disagree with that.  The fundimental problem with Wii Music is that you need to have some musical accument to actually really enjoy it.  Worse, it came out at the height of Guitar Hero/Rock Band, which were rhythym games not actually music games like Wii Music.  But they were vastly successful because anyone could pick up a guitar and quickly feel like a rocker.    Wii Music required that you pay attention, actually learn something and again, have some native musical aptitude.  If you went in with the GH mentality, it was just a God-awful noisemaker (and for many kids with no attention span that was definitely the case).

My point being, Nintendo had the right concept, a successful Wii Music would have catapulted sales even further, but the execution here was off.  It wasn't accessible like Wii Sports, Guitar Hero was.   If it had been a rhythym game (say Wii Dance before Just Dance) it would have sold 40m copies.

Nintendo fell because Wii Music was the last innovation they did with the Wii_ titles (the fact it was a 'flop' only compounded the problem).   Everything else was a lessor sequel (Wii Fit Plus, Wii Sports Resort (good but not as good as Wii Sports), Wii Play Motion).   Wii Party was somewhat innovative in how it brought the party literally into the living room but too little focus on that and NA was already party-game supersaturated which stiffled sales.   After NSMBWii there really was nothing for the Wii____ audience to buy.  Nintendo returned to catering to Nintendo fans only: SMG2, Kirby:EY, Metroid:oM, DKCR, Kirby, Zelda:SS, Kirby...

Nintendo themselves said 'they need to constantly surprise people' in order to keep their attention.  They didn't follow their own advice.  And WiiU isn't a surprise either.  It's just rifting off the popularity of tablets (to the casual observers eyes) not actually innovating in any way.

Considering people were used to Guitar Hero/Rock Band - even Dance Dance Revolution, the music selection on Wii Music seemed not only like a joke, but as a complete slap in the face.   You paid $50 to play free songs?  Really?  Even if Wii Music had done a straight dump of music from SSBB it would have been a 100x's better.    Heck in 2009 you should have been able to slap you're favorite's onto your SD card and played Wii Music with them (but no sharing of that content).

I never understood this decision, it just felt extremely cheap on Nintendo's part.

This speaks to why Wii Music 'flopped' (33 highest selling Wii game) with the general public. The game does not come into it's own if it's just just to play a song. You have to put your own creativity into the song to get into the true genius of the game. From that perspective it is too complex and not accessible enough for many people I guess. And young kids in my experience really can make Wii Music a pretty dreadful experience.

No matter what songs you put in the game, random spazing will not generate any joy.

I couldnt resist

I need to pick this game up on Amazon sometime soon. I was always curious about it but never tried it out.