The biggest factors are image and momentum nowadays. Had the Wii U launched with Super Mario Maker and Breath of the Wild, it would have sold bucketloads more than it did. And the Wii would have sold much worse if Wii Sports released a year after the system's launch. In that sense early exclusives are much more important than later exclusives, because they create the first real impressions of the console and those last for years.

The Wii U had the games it needed to sell well, but they came too late to save it. And even with some true killer apps at launch, Nintendo's mistakes like the bad marketing, weak CPU, and bad price would likely have kept it far from the Wii's level of success.

Also agree with the posters who said it should have continued to use the Wiimote and not try to reinvent the wheel again.

The PS4 is an interesting counterpoint to the 'exclusives sell systems' argument, because it actually took a while to start getting those amazing exclusives it has now but still sold really well without those exclusives. I remember the complaints of how bad 2014 was for so many people who had a PS4 and XB1 because very little was living up to expectations. That was when the Wii U started to get its killer exclusives like Bayonetta 2, Mario Kart, and Smash 4, but they came too late.

Exclusives sell systems when they come at the right time and in a sense blow the industry away. The last time that definitely happened was Wii Sports and Gears of War in late 2006. Wii Sports needs no introduction, and Gears just looked so much better than anything the PS3 launched with it gave Microsoft a huge edge for much of the generation. Had it released the following year, however, it wouldn't have had the same impact and the 360 likely wouldn't have had sold as well as it did overall.

Final Fantasy 7 is the game that put the PS1 ahead of the N64, which was actually outselling the Sony machine before then. Sonic allowed Sega to compete with Nintendo in the 16-bit era..

The only times late-gen exclusives really turned a console's fortune's around was Donkey Kong Country, which blew people away so much it allowed the SNES to pull ahead of the Genesis and win that generation, and Pokemon on the OG Gameboy. But other than that they don't seem to matter much. Perfect Dark and Conker didn't push the N64 the way DKC did. RE4 couldn't save the Gamecube. Mario 3D Land and MK7 did save the 3DS, but they came within the first year and still couldn't fully recapture the momentum that the system had lost.

I'm not mentioning just the systems seller, but any exclusive I can remember. Even with that the list is sparse. Just talk of the good ones and you can count them on one hand. Which is why I don't get why people think Wii U was a powerhouse for exclusives.

Still as for the OP the lack of games on it made it sell badly. It had barely any good games other than platformers and some bad third party ports before the release of Breath of the Wild which was hyped as a Switch exclusive.

Exclusives do matter. That's why the WiiU sold about 14M...

Xbox barely has any exclusives if any and we will never know how much Xbox One sold and will sell thanks to MS not releasing any numbers. As for Wii U there were more factors involed than just exclusives and let’s be real Wii U didnt have an Odyssey and Breath of the Wild Xenoblade 2, Spaltoon 2 type of games when it released the exclusives werent that great for Wii U they were fine but not great.

At that time there was an assertion that consoles were dead and only the mobile games market would exist. The result is that nintendo focused on 3ds and sony on ps4, the result was the death of ps vita and wii u.
Today, it is proven that the market of consoles will grow more and more, proof of this is that the 3 players are having great results.

Exclusives is a messed up word these days.
WiiU failed while it offered many console exclusives
Steam Succeeds relying mainly on Multiplat games.

Take your pick.

Would wii have taken off without the motion control phenom? Would switch without the portability factor? I highly doubt either would sell anywhere near as well. 

The WiiU had an identity problem TBH. I know people to this day that still think it is an add on to the Wii. Hell I know one guy who got it as a present and it just sat in his closet for years. When I told him it was a console, he was floored.

But really, people just cherry pick this argument to meet their own agenda. XBox fans say exclusives do not matter, but they lack notable exclusives themselves. Playstation fans praise exclusives overall, but when the WiiU failed they said exclusives do not sell consoles. They also said it during the first 2 years of the PS4 life during the whole, "PS4 has no gamez" debacle.

Then enter the Switch and they say it is only selling because of exclusives and the portability of the multiplat games do not have anything to do with it.  All of a sudden, it is about exclusives again.

At the end of the day, exclusives are not the only thing that sells a system, but they do play a MAJOR role.  As for people who say they matter or not, well it seems to me that more often than not they are only using the topic to further an entirely different point than the topic of exclusives themselves.

I think you're wrong. At least, that's not what that store wrote 

"The games with "Wii U" on it need the Wii U handheld and aren't compatible with the Wii console alone"

So if the Wii U was named Switch instead you think it would sell gangbusters?