Talk of reasons Wii U failed?
The name isn't discernible enough from Wii
"Wii", "Wii U". On one side you might say that "Well, Super Nintendo wasn't that different from Nintendo Entertainment System.", but that is in fact wrong. It isn't merely that Wii is quite similar in name to Wii U, it's that "U" isn't discernible enough on it's own. It also applies that letter after "Wii" and not before "Wii". A word like "Super" stands out far more as it implies whatever it is is far better.
So what this did was it made the casual audience think of the thing as nothing more than an add-on, and it really didn't help the system was so similar in design to Wii that even if a parent is looking at the box, they're gonna think it's just an add-on tablet for the system, thus losing a huge chunk of profits from the mass unsuspecting audience.
The system is too much and it's gimmick is undesirable with the way it was executed
With a price very unlike Nintendo, 350$, for the only SKU of the console anyone would actually want, it threw off the lower income audience that Nintendo thrived on last generation with Wii at 250$. Not only that, but the gimmick itself didn't revolutionize gaming in the same way motion controls did. Motion controls promised the idea that you were interacting with the video game as if it were real life, something every gamer dreamed about and any casual person could take part in as anyone can flail their arms around or shake with their wrists, whereas Wii U is just a tablet lodged into a controller that offered no real benefit to the mass audience nor even the core gamer audience, whilst only adding another 100$ essentially to the system's cost to users.
The execution was terrible as well as you could only have one tablet, thus the innovation of last-gen where anyone could jump in was lost and it was only exclusive to that one happy camper who gets the Game Pad. The streaming tech was nice, but with the range it could only be used in a limited amount of ways for most people, and even at that, streaming games to a big controller is only gonna appeal to a small amount of people as most people want to enjoy their games on their TVs. Not only this, but the controller is heavy, large, and is more of a nuisance than a boon for simply just playing video games. They gave us options with a Pro Controller, which is what people were wanting, but some games couldn't use it, and some games cannot even boot (Shovel Knight of all things!) without the Game Pad, despite the games not needing it. You can't even change your system settings without it, and initially you couldn't even purchase things from the eShop without a Game Pad.
All in all, the execution of this idea was completely flawed and I'm glad the Switch did it correctly.
The system lacks power
Now although this won't bug everyone, it'll still make people hesitant to purchase said product if last-gen systems like Xbox 360 and PS3, which sold quite a bit, it can't very well out perform at any noticeable level. The Wii got away with this because the remote was such a strong enough gimmick for it to work, and when the gimmick doesn't work, you get Wii U.
The account system and OS are prehistoric
NNIDs are non transferable with the Wii U unless you have two Wii Us present, you cannot simply just take your NNID to another system and play on it like you can with a Gamerag or PSN ID. So what this does is, let's say you want to play a game with a friend at their house and not have to drag your system over and play on theirs, you will miss out on unlocking certain things in games or achievements because you can't simply connect to the network and download your profile. Not only this, but if you sell your Wii U, you're pretty much SoL if you want your games back if you buy a new system later unless you send that very console to Nintendo and ask them to put your NNID on there with your games. It really is just...so archaic by design.
The OS locks System Settings and certain games to the Game Pad, despite the very fact that you can use multiple controllers in said games as stated earlier, but we also also have some very anti quality of life messaging on this system. You have to hit the menu, boot into Miiverse which take several seconds, THEN go to direct messages and send a message on their Miiverse, you can't just simply message someone easy by hitting the Home button like you can on any other system of this gen, and PS3 and 360 of last gen. Talking with people you meet is a chore, there is no real way to voice chat conveniently outside of a app where you have to video chat via a Game Pad in face. No party system, no private chat system, no nothing.
You can't play music files, you can't play video files, your only options are basic streaming apps that are just the accepted norm on any modern device these days.
Last note
So yeah, I kinda wrote a lot here but I felt it neccesary to really get across why this system failed. It lacks everything desirable about a system outside of having some really good first party titles.
Super Mario 3D World didn't make as equally big impact compared to the Galaxy games, plus Paper Mario Color Splash was still not what fans want. Super Mario Maker lost its exclusivity.
