The publishers are trying to provide what Wii owners have demonstrated they wish to purchase. They're not going about it wrong, nor are they guilty of "not trying" -- that's ridiculous. Every Wii game developer wants to see their game on top. Every Publisher wants every game to perform in a stellar fashion. They do the best with what they have (usually this means "what they have to spend").
Wii games have gotten a lot less to spend than HD titles (@MaxwellGT2000: I have never debated this, btw -- go read my posts carefully. I have always stated that publishers need to invest more in the Wii if they want quality titles, and have never doubted that publishers are telling the truth, that Wii development is lacking, in terms of development money. Those numbers were always averages, and averages are heavily skewed by the sheer mass of shovelware).
Now they've come around, and are realizing they need to invest in the Wii, on a per project basis, to have any chance of succeeding with it. You still aren't going to see M-rated titles. You're only going to see the kinds of games that Nintendo, and eventually other 3rd parties, has/have proven to work. Investing more means they will play it even safer -- just like they do with HD games. Shooter after shooter after shooter on the HDs is safe. A lot of the cheapest dev teams (i.e. ones in Eastern Europe, HK, etc.) have really started to nail the common HD genres, so there will always be a plethora of cheaply-made HD shooters, etc., as well.
You can probably expect mostly platformers, fitness titles, party games, brain trainers/puzzle games, and youth-oriented games of all sorts on the Wii from now on -- anything that's been proven to work with the everyone/youth demographics. License titles will remain as-is, although the smaller licenses will probably dry up. You'll likely also only see huge toy and movie IPs from now on, which will cut the shovelware percentage down immensely.
If any M-rated game IPs ever become popular on the Wii, they'll have to be a breakout titles that had a low budget in its first iteration. Something small but cleverly made -- perhaps as WiiWare. The publishers won't risk putting a spendy M-rated title on the Wii without serious franchise backup (like Call of Duty, which will probably continue to eek out an existance on the Wii, albeit in delayed or crippled fashion).