A lot of people don't buy the Wii U
Because they don't know it's a new console.
With a name like Super Wii for example
Nintendo could have sell millions of copies more.
it's just like Nintendo and Super Nintendo.
Try to think about Nintendo 16 bit system Super Nintendo.
Instead of Super Nintendo they would have call it Nintendo U.
A lot of people would probably think Nintendo U is the same console as the old 8 bit system Nintendo.
The names are too similar.
They did a smart thing of not calling their 16 bit system Nintendo U.
They called it Super Nintendo.
The same thing should have been with the Wii and Wii u.
Instead of Wii U they should have called it Super Wii.
the name wouldn't have confuse anyone and they would sell many more copies.

It still does not have the sufficient market recognition among the casual consumer. Hell, when I was preordered MK8 earlier this month at EB Games, I was disturbed by the fact that there had been people who went to preorder it and were trying to do so for the Wii. There had also been a mother who attempted to buy her kid a SM3DW and didn`t  realize it was for the Wii U (the employee had to explain to her). That is the casual market.  The naming and lack of marketing is why the console has not took off.

Nintendo
Nintendo U
Nintendo 64
Nintendo 64 U
GameCube
GameCube U
Just to let you see how similar those names are.
Does it sound or look to you like a name of a new console?
It's practically the same thing!
With a better name Nintendo could have sell many more copies.

Yes, but I'm not sure that much. But if they released Smash, Mario Kart, and NFC in the first year, things would be MUCH higher. Even though it will still get a bump from those titles, it's too late and the Wii U is associated with poor sales and failure. It could have been different if they got their big titles out sooner, instead of niche titles like Pikmin 3.

Well, that depends on the new name. I think it's safe to say it wouldn't have sold the same though.

The Wii U is great console
The sales for their console could have been much better if they would choose a good name.
The first thing a company that releases a new console should think about is the name.
Let's hope Nintendo would choose a good name for their next console.

There are many ways to make the customer understand you've got a new product.

A new design : failed
Buzz on the internet, word of mouth : failed
A powerful product : failed
Good ads : failed
A good name : failed
A clearly different product/games : failed
A bunch of new games at launch : failed
Lot of happy customer hungry for your new product : I suppose it failed

Don't blame the name.

I really can't believe you can have 120 millions of happy customers, 20 of them fans of the brand, have a new product good enough for them, and you don't sell well because of the name. Even if it was for the confusion on the name, (I don't believe that but) the casual public saw multiple time the ads, with supposedly a new gamepad and new games, a name "Wii U" appeared... About 90% of them thought it was just a new gamepad, and 95% of them thought "whatever, I don't give a shit". They didn't think that's a new console, they didn't go ask to the shop for the new pad, didn't search on the internet, didn't ask to a guy that knows, whoever understood didn't dare talking or buzz about it. That's a severe problem, and that's what the problem is. Your naming problem is totally delusional. And I do hope Nintendo thinks better about that, because if that's the way they think, like it's just a little misunderstanding on a very little and stupid naming mistake, they are dead.

To address the first part of your response: 

New Design: Apple has proven that is irrelevant 

Interent Buzz: The name plays apart of that as well as poor marketing

A Powerful Product: Substantially more powerful than it's predecessor

Good Ads: Agreed, as I said marketing plays a significant role

Different Games: Have you even tried the Wii U?

New Games At Launch: Substantially more than PS4

Customer wanting product: Again poor marketing resulted in lack of consumer knowledge

I'm delusional? You obviously do not have a grasp on the basis of how marketing works. A poorly named product that does not clarify to the customer that it is a different product than it's predecessor is not going to acheive awareness and sales with the casual consumer. Simply naming the Wii U "Wii 2" would have allowed for substantially higher sales (I'd estimate the ltd would be around 12 million at this point) and led to a lot less confusion. Hell, even major news networks (CNN) ran storys about hte Wii U being an add on. People are not going to pay $349 for an add on.  I find it amusing that you do not believe the naming of a product matters. Why do you think companies like Sony, Apple, Samsung do so for alot of their electronic devices when releasing a predecessor? Because it's easier for the casual consumer (which is a large basis of Nintendo's base) to be aware that it is different from the previous entry. If Nintendo wanted to continue the Wii name, they should have used numerals until the third or  fourth iteration before changing it to something like Wii U.

A simple marketing decision of putting 2 instead of U could have made all the difference.
Wii U is really confusing name.
It is practically the same as Wii and what is U anyway?
confusing your costumers so that they won't buy the console?
I'm sure that wasn't Nintendo intention with that name.
It was simply a bad marketing decision.
Wii 2 makes a lot more sense.
Imagine PlayStation 2 was named PlayStation U.
i'm sure It would have sell much less copies.

Definelty higher. They probably wouldn't be that much higher, but many people do think the WiiU is some extension to the Wii. That is the downside of selling a bajillion peripherals.