Yeah, if you're going to call Wii Fit and Wii Sports shovelware, don't expect people here to take you seriously. As for people playing Wii Sports only due to the pack-in, Japan's 46% attach rate says otherwise.
You're asking why Metroid Prime 3, Mario Galaxy, and Twilight Princess is seeing poorer sales - it's pretty simple. The franchises have gotten relatively stale. Metroid Prime, Mario 64, and Ocarina of Time were all must-have titles, as they were the first 3D iterations of the series. In case you didn't notice, Metroid 2 took a sharp decline in sales, as did both Mario Sunshine and Windwaker. Still, the Wii versions of Brawl, Mario, Kart, Zelda, Metroid, and even RE4 have/are going to outsell their previous iterations by a large margin.
Btw, Twilight Princess was released on the Gamecube, as well. It sold 1.56m copies, nobody is going to buy the same game twice.
You can whine about the console being a shovelware magnet all you want, that isn't stopping third parties from releasing games like NMH2, MadWorld, The Conduit, Dragon Quest X, MH3, etc. on it. They have acknowledged there is an audience for these games, regardless of what you think.
