what exactly did the Wii have that would make lots of people buy it?
Resident Evil that was on rails shooters.
EA simulation sports games that had cartoony childish covers. For all we know that cover wasn't tiger woods but one of the illegitemate secret children he fathered.
The COD that defined the franchise skipped the console then port come two years later.
The best efforts on Wii from 3rd party were PS2/GCN ports like RE4, Godfather and thats about it.
A few of the Fifas flopped, some of the Maddens, WWE also sold very averagely. 007, Need for Speed, Top Spin, Manhunt, Tiger, Bully, Silent Hill, Tomb Raider, Some Guitar Heroes, The rest of the maddens and Fifas, DiRT, a lot of the major movie tie-in games, a lot of other major sports franchise from EA and Take Two (NBA & NHL), SSX, Dead Rising, Tony Hawks, Alone in the Dark, Pro Evo, Scarface etc all flopped super hard. I'm sure theres more.
These are major franchises that did a lot lot better on other franchises. The game needs to sell enough to cover the extra development costs and costs to get it to market. If they get burnt once with poor sales then don't expect them to get burnt again. In the end some publishers worked out what games sell best on Wii and the majority of the best selling games from third parties is party, music, dance or exercise games. Publishers also worked out that they need to make some of there games appeal more to families to sell, hence the adapted versions of the full fat version.
Now couple the fact that 3rd party games (outside of the "family" bracket) sell poorly on Nintendo and that the Wii U sales are abysmal, 3rd parties are less likely to support. I'd be surprised in PC sells more that a couple hundred thousand on Wii U so it's kinda great that they still choose to release it for the Wii U even though the guys comment wasn't very nice.