Actually, I'm pretty sure adult Nintendo fans outnumber kids on Wii U. 

If Wii U was effectively tapping into the "parents buying for their kids" market, its sales wouldn't be so dismal.

It also had 10 times the promotion.

That doesn't change the end result. Such a big difference can't be put down to promotion alone.

*Takes a look at Splatoon sales*

I disagree haha

Not a dinosaur. Nintendo confirmed this. ;)

Tropical Freeze is the second game in a series and I think that a lot of people had their fill with DKCR on the Wii. Tropical Freeze doesn't really do anything to stand out as an HD game, and so there's really no reason for a lot of fans to come back to DKCR on the Wii U unless you are a big fan of the gameplay. It would be different if they did something really compelling with the gamepad.

I think that it's almost the same situation with NSMBU. If I owned the Wii version of New Super Mario Bros, I would feel absolutely no desire to buy it again for the Wii U since it's basically just a slight upgrade to 2D graphics that I felt already looked good on the Wii. I think that if it wasn't for the mandatory Wii U bundle and the fact that it was basically the only Mario game available for the first year on the Wii U, I think NSMBU would have been an unsuccessful sequel for the same reasons as Tropical Freeze.

Yoshi's Woolly World, however, is a game that really stands out in HD and while it doesn't really change the gameplay of previous Yoshi games it does so much cool stuff with the yarn aesthetic that people are still excited. When you combine the cute factor, a very creative Amiibo, and a stunning graphical art-style people are going to be excited to buy the game just to see some of those creative visual implementations of the yarn aesthetic. When I hear about Velcro conveyor belts being used in one of the levels, I just want to buy Woolly World so I can immerse myself in that environment!

There was absolutely no buzz surrounding the Wii U at the time of Tropical Freeze's release...
Relative to the amount of buzz there was in early 2014, there's way more buzz now...
In the grand scheme of things, however, there's still next to no buzz surrounding the Wii U...

Promotion isn't the only reason for Splatoon's success. The game has plenty to sell itself on already; its highly accessible, it fills a vacant niche on the console, and its word of mouth is very positive.

Three things: lower price point, Yoshi amiibo, and a release date amongst a strong 2015 release schedule allowed Woolly World to move more units.

That's good, should be a Million seller