Hear me out, okay? I always hear people point to the GamePad itself as the reason why Wii U failed: it drove up the cost of manufacturing (and consequently the MSRP for) the system, it scared off third-party developers not looking to deal with such overly convoluted technology, the system never really demonstrated why the GamePad needed to exist, and so forth.

However… just look at the limited specs of Nintendo Switch 1 & 2 in comparison to the competition. Do we really believe that the GamePad was that much more convoluted than developing for a system only capable of running Dark Souls at 720p on-the-go? And how come the DS and 3DS saw such strong third-party backing despite not only having the same issue of a second screen, but also far greater limitation on specs?

While I do not deny the need for the GamePad’s existence was never truly justified in the software, it was an innocent little accessory that — if really necessary — could ultimately be ignored by third-party devs. The Wii U’s issues go well beyond the GamePad.

Thoughts?

I think the gamepad still was one of the main factors why WiiU did not succeed. Not because it was bad, I think the pad was well designed. But it somewhat felt like they designed the pad before they conceived the game ideas that needed it. And the marketing almost exclusively focused on the pad leaving the actual console in the shadow.
So I think the pad needs to take some of the blame even if the tech was good and using it was comfortable.

You are correct ;)

With gaming, the reasons people give for the success and failure of consoles are usually wrong. Or they're failing to tell the whole story. In this case, the main reason why Wii-U failed was timing. Wii kids were still kids, just older. And when you hit that in-between age, you tend to want something a little... well... grown up. As gamers, we all know most of that is BS, that a great game is a great game etc. But not at a certain age. And this is why the Switch mainly exploded (and why suddenly, all those Wii-U titles that nobody wanted became best-sellers). The kids that were raised on Wii were suddenly in college, or out of high school, far enough away from their own faulty pathology, and with some of their own money to boot. It wasn't the form factor, although that did play a role. It was the timing. It's always about the timing. Always.

Also, if a console can pick up the "thing to own" moniker out of the gates, it's pretty much set in stone to succeed. People love to be cool. They need to be cool and accepted by their peers and society. So as soon as something becomes that, forget about it. The rest can just go take a lunch. It's over.

It was really a perfect storm where almost everything went wrong.

The Gamepad was a mistake in that it added to the system's cost while not really being a selling point for most people, but the long droughts, dreadful marketing, silly name, and a myriad of other factors all came together to spell doom for the system.

The GamePad was not the biggest reason the Wii U failed, but it is an issue. Driving up the cost of the console was a huge problem.
Wii U was rougher to develop for than Switch because of its PowerPC architecture and weak and slow CPU. Those were much bigger issues for developers than only 2 GB RAM and the GPU.

It's always about the games.

If the Wii U launched in its first year with Breath of the Wild and Mario Odyssey, it would perhaps not have reached 100 million, but would have gotten momentum so 50-75 million should be possible.

I strongly agree it was a major reason for the failure simply based on the negative reaction around the Gamepad through the generation. The word "half-baked" was used a lot to describe the Gamepad and Wii U experience. It was definitely the source of a lot of negativity around the Wii U.

• Off-TV gameplay lacked basic desired functionality, this was a big complaint (even addressed in the Switch marketing with it's alternative "handheld mode" (toilet guy). Basically, if you left your living room, the Wii U Gamepad ceased to function.
• It had a terrible battery life compared to other home console controllers.
• It was very clunky for a lot of the games that Wii Remotes worked so well for. You basically had to acquire them separately if you didn't have them.
• Unlike the Switch 2's backward compatibility being fully functional, the Wii U gamepad was unusable on your Wii library. You needed to keep old controllers around, this did NOT feel like a continuation of the Wii the way the Switch 2's full backwards compatibility did.
• The whole idea of dividing your attention between two screens out of your range of site made for intrusive experiences throughout games that didn't require them but added them anyway.
• The whole idea of "asymmetric gameplay" (unlike the Wii) actually did feel like a gimmick to cover up the fact that only one gamepad could be used.
• The Wii U felt like a one player home console because of the Gamepad.
• It was bulky, didn't look very fun to use, people at the demo kiosks often looked like they were handling something weird when they picked it up, it was a full 180 from the Wii Remotes.
• It was uncomfortable to play the Wii U gamepad at the demo Kiosks. It wasn't a good experience

But personally, I think there are other big reasons for the Wii U's failure: the Kiosk experience being a big one (which I touched on above). While these had worked very well in the past to demonstrate new consoles and features all the way back to at least the later years of the SNES, the Wii U did the opposite... and not in the Saturn way, where people liked the kiosks, but then saw the price compared to the Playstation doing the exact same thing, and bought that instead. Simply, the Kiosk for the Wii U was a bad experience, it probably advertised people to not get the console.

Apart from the Gamepad just feeling clunky at the Kiosks, the load times were crazy... like 2-3 minutes to get into a game. And the landing times in the early days of the Wii U weren't much better, and even at the end of the cycle, it was still quite long compared to the Wii and the Switch, where you can just turn it on and play.

And the third part was that it wasn't so much that the games were bad, but that they were bad for that console. Most people don't like Mario Kart as a one player game; most people don't want to sit through all the Wii U OS loading times and Wii Mode loading time to play Virtual console games they could have done instantly on the Wii or previous consoles; and most people prefer it when their home console's controller lasts more than 90 minutes. This was demonstrated when Mario Kart 8 became a major sales driver for Switch alongside Breath of the Wild (also on Wii U, also a failure there), people wanted Mario Kart on that console, not so much Wii U.

As a very hardcore Nintendo fan, it was really hard to see them fumble this one so badly, because Iwata outside of that had done a great job; even cleaning up the disastrous (and unpredictable) 3DS launch, which suffered a huge amount of "3D will destroy your vision and give you migraines" hysteria at launch... Although, it was destined to lose a lot of users from the DS because of the rise of smart tablets and mobiles. Some lost faith in Iwata over this, but the extent of his health problems weren't known at this time, which may have contributed.

If it's not clear. From everything I saw and experienced, the Wii U Gamepad was certainly a major cause. And I find myself not being able to look back at it with the rose-coloured spectacles a lot of the fandom has decided to do (Gamecube all over again).

Strongly disagree about this. Asymmetric gameplay was one of the smartest ideas of the Wii U generation and it is a great pity it has essentially been abandoned since. I don't understand why Nintendo has not pushed for more games where you need a docked Switch and a handheld Switch, with asymmetric gameplay between players. 

It was not only the gamepad, that's for sure, but the thing drived the cost of the system up so much that it became a problem, and it was rarely used very well.
Other problems were the hardware itself, the PowerPC architecture was just too outdated and weak, even if the system otherwise was capable enough. The name also sucked, which was an issue. Most importantly though, the marketing was a mess!
It's a bit of a paradox really, Nintendo couldn't sell the gamepad idea, but if you don't have the gamepad you are essentially just selling a PS3 in 2012, but without the multimedia functionality. That'll never work.
The gamepad caused the Wii U to fail, but it was also the key for potential success, had they sold the idea well. They needed more games that showed what the idea could be used for. Nintendo Land and Mario Maker were great, but there were just not enough big titles like that. The biggest missed opportunity was exploring the non-gaming features - having Spotify, Netflix and all the other popular streaming apps that were booming at the time could be a big win for a system that can so conveniently be navigated with a tablet interface while natively connect to a big TV and a sound system. I know Netflix was there, I really enjoyed using it that way, but I saw very little marketing of that feature, and most other big apps were missing.

True to a certain point. The tablet being essential to the WiiU was a massive weight to the system. If the WiiU had been able to lose that weight the same way the XBOne did with the Kinekt 2, they could have easily sold the system at 50-100$ less. But yeah, the poor WiiU had a plethora of problems.

The fact it never had a "All I want for Christmas is U" ad is criminal.