Wii didn't getr good third party support for three reasons:
The first reason was that everybody saw the Wii falling to a distant third place this generation. As such, they figured that they would make more money by supporting the two HD consoles.
The second reason is that once developers saw that the Wii was doing well, they decided to support it with the wrong types of games. They had second and third string development teams make "casual" games for some easy money. The games didn't sell, and developers were out of money.
Third, they put all of their main franchises on the HD systems. So now, they are stuck on those systems as that is where all of their customers are. If they switched over to the Wii now, they'd just sell less than they would on the HD systems since they would be effectively fragmenting their customer base. Someone who bought a PS3 for Metal Gear probably isn't going to buy a Wii to play the next installment of Metal Gear, for example.
So, third party support is limited to spin-offs of main franchises and new expanded audience games. Ubisoft got a smash hit with Just Dance on Wii for example, but Assasin's Creed will never sell that well on Wii since most all of the AC customers are on 360 and PS3. Wii won't get the next installment of FF, and offshoots like Crystal Chronicles will continue to do relatively poorly.
