I read a pretty recent article where Iwata explained that Nintendo does some types of games really well but other types of games not so well which is why they need third parties who are good at those types of games. He also said that Nintendo development teams are already stretched thin which is why Nintendo primarily focuses their own efforts on getting those core franchises out that people want from Nintendo. This is also why Nintendo have been expanding their development team recently.
I think Iwata has actually been on point with a lot of what he has been saying recently and if Wii U had real third party support and not just ports of old games it would actuàlly be a very appealing console. But I can't blame third parties for not supporting it considering the user base is so small. Truthfully the problem with Nintendo is also the reason they sold so well, a lot if gamers are happy to pick up a Nintendo console as a secondary console so they can play those Nintendo exclusives. While this means Nintendo consoles and first party tiules sell we'll it also means third parties don't sell as well. And it's not that Nintendo gamers don't buy those third party miltiplatformer games, they just buy them for the other console they own.
they need to change the perception of their brand to be more inclusive to today's trends in gaming. go out and get new development studios to do more mature games and draw in a more mature audience so third party developers will say "hey their audience is expanding" and make games for them.
every console since the Nintendo 64 has suffered from the same third parties don't really wanna touch it issue. the fact of the matter is the core Nintendo crowd aren't enough to demand third party attention.
there's people like me who i buy Nintendo systems only to play Nintendo games and that's about it. they aren't going to be as successful if the only people who buy their consoles are gamers picking it up as a second or third system just to play Nintendo games.
sure the Wii's motion control gimmick brought it some success but outside a very small number of games like Just Dance the third party success on the console was a barren wasteland.
people like me are never gonna buy a Call of Duty game on a Nintendo platform because its not the only console we own and its no serious gamer's first choice to play a game like that on. i don't even know why Ubisoft is bothering with Watchdogs cause the Wii U is gonna be the last platform anybody is buying that on.
