Why is so hard for Wii U sell 20,000,000?

[captain carot]

It's just two and a half years, though i'd basically would agree.

Console sales would have to explode, that's unlikely. Instead, every Nintendo home console in the last 20 years sold best in the first years with heavily diminishing sales after four years.
So even with Wii U getting a successor in 2018 it seems unlikely that it will sell well from 2017 onwards.

Now, how long will it be produced and sold? The Gamecube didn't work to well for Nintendo. So they stopped production just after the Wii Release. Wii U sells worse, though, because it's expensive to manufacture, at a much higher price. Again, seems unlikely that it's produced longer than until early 2019. Depending on U's on the shelf they might even stop production before a successor arrives.

If it where possible for Nintendo to sell Wii U for 149,-€/$ from Q3 2015 onwards, well then i could see it reaching 20 million.

And by the way, they had it in their hands last year. 249$/€ pricecut, SSBU coming at least one or two month before SSB3D, Xenoblade X out in Japan in november/december etc and Wii U might have reached 12 million last year. But it didn't.