MK8 attach rate:
JP: 25%
US: 50%
EU: 60%

It's not just the Wii U though. While PS4 titles have much better first weeks, sales tend to drop like a rock, so much that very few PS4 titles even chart longer than 2 or 3 weeks. Only 3 million PS4 games have been sold in retail, less than 3 per console, and it doesn't look like this will change much yet. 33k PS4 sold and 118k retail games, so just around 3.5 games per console, 7k and 27k for the Wii U, which ain't much better percentage-wise and much worse in absolute numbers.

In other words, this seems to be more of a general trend in japan, which is most notable on Nintendos console but not exclusive to it.

variety is good.. but most of first buyers are mostly hardcore fans.. when the more casual* come we will see more variety I think.

*casual (for me) = The ones that see a special game/s and buy.. and where the price and "wow" factor means more than brand.

And the tread is strange..  like not making sense..

Do you mean that more games over 25% is good for "variety"?

And what is "variety" in userbase to you.. becourse as i say.. first come the hardcore.. then come the rest.. and we are just started that "fase"

MK8 is close to 50% attach rate but I just put it under over 25%

Most of wiiu owners in japan are kids, the statistics say

You forgot the nuclear bomb Wonderful 101, considering more than a few games on that list are either partygames or platformers I don't think Japanese customers need to do anything, but Nintendo should offer more variety of that I am sure. The gamecube wasn't a beast in sales but it had more variety of great games than the Wii U will ever have with the current trend. Sure MK, Smash, Super Mario, Zelda, Mario bros and in lesser extent Pikmin sell great, but that is no excuse to devote yourself almost entirely to those IP's or Genres they repressent. W101 and Bayonetta 2 where good examples of how not to do it even though they where good games, they lacked either good advertisement and bayo 2 a link with the audience intended. 

Nintendo needs a new IP like Splatoon and advertise it well, as a new metroid and a completely new IP which perhaps involves a more emotional WOW type of game and making that character the wii u mascot. Because even WII U's games are good not a single one of them is redefining anything, they are just really good in their safe respected genre. This gen needs something like pikmin or metroid prime was for the gamecube an eye opener to give gamers a NEW experience, not a good but also thrusted one. The W101 tried (and used the tablet pretty well, should've been a launch game), but since ninty failed to advertise this and choose for a bit particular targetgroup, they need something new.