Go and see the list of million sellers for wii for yourself, and apart from some of the nintendo publishes games most of it is garbage, there is a lot of garbage also on the 360 and ps3 list, but not to the extent that its present on the wii list
Going from that list, what 3party developers think sells on wii are, gim simulators , minigame compilations and music games, (apart from the nintendo published games )so thats what they are trowing at the wii at the moment. But that is already starting to fail, the market is so crowded on the genres that nothing that launched on the last months is selling well. ( infact the only games selling at the moment on wii are the usual 5 franchises that have been selling for years now )
So if i were a 3party publisher right now the only thing different i would do was release a game similar in concept with mario, a platformer and see if that could catch a bit of the mario craze and the fact that practically nothing similar to mario exists on the wii at the moment and that is something that has intrigued me ever since the wii became a massive hit why didn't anyone tried to revitalize platformers, sonic doesn't count, its more of a racing game then a platformer