It's because the vast majority of Wii U owners are the core multigenerational fans of Nintendo consoles. On Wii those fans got lost in the casual noise. If you actually think about the demographics of the owners of Wii vs Wii U it's not at all surprising that 3rd party "mature" games will sell relatively better on Wii U compared to Wii.
However there's also the sad fact that Wii U's highest selling 3rd party game has sold less than 600K. Whereas PS4 already has a 3rd party game at >1 million and it has a total of 4 3rd party games over 600K. With less than a month on market. Xb one has 2 3rd party games over 600K.
When you get around to being able to compare 3rd party performance by the time Xb one and PS4 each get to 4.5 million in sales the Wii U's 3rd party performance at the same level of sales is going to be embarrassing.
In reality there's actually nothing particularly positive about 3rd party game sales on Wii U.And 3rd parties are already looking at PS4bone game sales and seeing that their bread is going to be buttered on the PS4bone side this gen.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix








