There are two important elements at work with this:
A) Nintendo needs content. Alone, they can't produce enough games to counter the content difference provided by third-party publishers and developers on Playstation and Xbox.
B) Nintendo fans, in general, are bound to Nintendo by some kind of blood oath. Had Wonderful 101 been Mario's Heroes, it would have sold exponentially better. Third-party developers know this. Allowing them to apply Nintendo skins to their own games should increase sales of those games enough to make them worthwhile to produce. Disgaea on Nintendo? Sub-par sales. Mario in the Underworld? Millions of copies sold. Persona on the Wii U? A waste of time. Link's Summoning Mystery Adventure? Record-breaking.
Actually, the second one sounds pretty good ...
