I'd say because they are highly accessible and/or are big name franchises (i.e Mario).
Halo and GTA have the later, and a large part of their success is that they achieved the former from the start (I've seen "casuals" become "gamers" because of Halo and it's not exactly hard to kill people and hijack cars in GTA). That's what alot of game lack.
It helps that we don't get a new one for X amount of years. I'm sure if GH was once every 3 years (with an awesome version each time) it'd be in that category, but since it's a yearly thing, the sales are spread out per version (and thus less impressive as stand alone games sales wise). Same with Call of duty.
Nintendo does it best because we only get 1 or 2 games from a franchise each generation. So a person who buys a Wii in year 6 is still going to pick up Super Mario Galaxy because there's been no other super mario game on the Wii. By year 6, Halo would have had Halo Wars, Halo ODST and perhaps even a Halo 4, GTA would have had the 2 DLC expansions and maybe even a GTA: Insert City here game by then.
On top of that, one thing the "core" developers need to do is post-purchase support. I guarantee you that had CoD:WaW not come out and Call of Duty 4 got another set of map packs, it'd sell as well as most of Nintendo's games, perhaps even better.
I can't say for sure why Wii music hasn't caught on fire, but I'm guessing in an age of Guitar Hero and Rock Band, a music game like Wii music that isn't super accessible (have you played the drums?) isn't going to fly. Wii Fit didn't have much (if any) competition for fitness gaming software and Wii sports provided us with a new way to play particular sports. Wii music doesn't do that because we've been playing the guitar and drums in arcades (and now homes) for years now and it just doesn't do anything better.