Do you have any idea how this could be changed?

There are two reasons for it:

First: Nintendo is an insanely successful game maker.

Second: Most high prolific games aren't releasing on Nintendo platforms.

See, Ubisoft would have much higher sales on Switch, if the had released Destiny, Assassins Creed, For Honor and Far Cry. Because currently these high profile IPs add to the sales for Ubisoft games on Switch... nothing.

Yes such an easy task to release those games on Switch right? Just row a slider and done.

You can fairly compare only the games released on all platforms: Just Dance, Fractured but Whole, Doom, Skyrim, Wolfenstein. Many of these are old ports. Hmm, VGC has no data (yet?) for Switch sales of South Park and Wolfenstein. For Skyrim I gfo with the special edition as the release for PS4 and XB1.

So, do 3rd-party games sell worse on Nintendo-platforms? Yes. Is it that bad as painted by the data cited by Meggiddo? No, because that is because many games are not released on Nintendo in the first place. So, the 70% market share is because the other game makers leave the platform to Nintendo. What should Nintendo do? Not release games?

10 games showed as third parties show the 90% of SW released? Nope. Are all the rest garbage level that no one would buy? I doubt it.

So, these numbers do indeed explain why 3rd-parties are shy to release on Nintendo-platforms. No need to angle for power-explanations or conspiracies or anything. But the dominance of Nintendo-software is because basically so many games are missing on the platform.

We will see more data in the future, with more multi-platform releases like Dark Souls Remastered, Dragon Quest XI and so on.

You know that Nintendo dominance on their HW goes way back to when games started being multiplat right? And I particularly have no issue with they selling good on their HW, after all they make their HW to tailor their SW.

The only issue I have is people that think the 3rd parties doesn't release because they want to screw Nintendo over. Power helps the problem (the easier to port, the less it will cost, most likely to get released), lack of market interest in the platform helps, bad relationship of the past help. Nintendo can't solve the power problem in a HW already released. But they can work out APIs that would make porting simpler, they could negotiate some high profile games to be ported with their help (which as far as we know they don't do, Sony done a lot on PS3 and I think MS also does) or funding.

Square Enix is wrong.
ARM and Maxwell is extremely different to x86 and Graphics Core Next.

The similarities that the Switch and Playstation 4 have is actually on the software side... Both leverage a *nix derived OS, both share common API's like OpenGL and Vulkan.

This. It all comes down to whether it is financially feasible, said feasibility will obviously increase with the more hardware units that have been shifted... To the point where sometimes companies can justify creating a game+game engine almost entirely from scratch to take full advantage of said lower specced machine.

PC gets the majority of Multiplats? Very rarely does the PC miss out on a big AAA multiplatform exclusive.

Well. Yes and no. It has some technical showcases that can't be ignored.
But the main reason why it got a port to the Switch was because it was a 60fps title, there was tons of room to move by cutting that down to 30fps and making some visual concessions elsewhere.

The big strength the Switch has is that from a GPU feature set perspective it is equivalent (And in some aspects exceeds) the Xbox One and Playstation 4... Which is something the WiiU or Wii didn't share.

Flops is a theoretical performance ceiling and not representative of real-world performance.

I agree, but Madden is a bad example. Madden is EA, and EA and Nintendo are special somehow. I never really saw a good support by EA in recent generations. But Ubisoft and Activision are more neutral to Nintendo (Ubisoft even somewhat positive), and they release some bigger stuff - but by far not all. For instance Ubi has Just Dance, Steep and Mario+Rabbids for Switch, but not Ass Creed. I think porting cost vs. expected sales make this a too hard decision. It might or might not change with a bigger userbase.

There are two reasons for it:

First: Nintendo is an insanely successful game maker.

Second: Most high prolific games aren't releasing on Nintendo platforms.

See, Ubisoft would have much higher sales on Switch, if the had released Destiny, Assassins Creed, For Honor and Far Cry. Because currently these high profile IPs add to the sales for Ubisoft games on Switch... nothing.

You can fairly compare only the games released on all platforms: Just Dance, Fractured but Whole, Doom, Skyrim, Wolfenstein. Many of these are old ports. Hmm, VGC has no data (yet?) for Switch sales of South Park and Wolfenstein. For Skyrim I gfo with the special edition as the release for PS4 and XB1.

So, do 3rd-party games sell worse on Nintendo-platforms? Yes. Is it that bad as painted by the data cited by Meggiddo? No, because that is because many games are not released on Nintendo in the first place. So, the 70% market share is because the other game makers leave the platform to Nintendo. What should Nintendo do? Not release games?

So, these numbers do indeed explain why 3rd-parties are shy to release on Nintendo-platforms. No need to angle for power-explanations or conspiracies or anything. But the dominance of Nintendo-software is because basically so many games are missing on the platform.

We will see more data in the future, with more multi-platform releases like Dark Souls Remastered, Dragon Quest XI and so on.

I would certainly hope if Fortnite and GTAV came out for the Switch this year that they would top 1 million.

That's only like 5% of the userbase. It would be astronomically pathetic if such big games couldn't clear that mark, especially since one is free-to-play.

At first glance, it's easy to dismiss the Switch as yet another first party-centric Nintendo console as it's so far not been able to get a whole lot of third party multiplatform titles from PS4 and Xbox One. You could say that its because NIntendo chose to make another under-powered console and that they should've made a PS4 killer if they wanted third parties. While that sounds good on paper, many gamers forget, or don't want to admit one thing regarding third party support. Developers, actually don't care about power that much. 

Now this doesn't mean power isn't important, it's always important. But ultimately, its actually one of the least important aspects when it comes to developers deciding to support a console. A console's third party support actually has little to do with how powerful it is. It has more to do with audience, user-base, ease of development, and any unique gimmicks or features. Take the Nintendo DS for example, yeah compared to the PSP, it was woefully under-powered. But to third parties, that didn't matter. Why? It sold 150 million units worldwide, a diverse range of consumers buying different kinds of games for it, had a bunch of then innovative tools to play with such as the touch screen, the graphics were good enough for most genres, and it was easy and cheap to develop for. As a result, it received just as good, in several cases better support than the PSP. 

Now I know some of you will try and use the Wii as a counter argument, but the Wii had a whole different set of issues regarding third party support. First, the console wasn't developed with HD in mind, which meant it lacked the shaders and development tools needed for HD games, which often meant porting to the Wii required re-developing the game from scratch. The Wii Remote and Nunchuck also had a limited button layout, which meant the control schemes would've had to have been drastically reworked, often giving certain actions to motion controls, which for certain actions and uses, aren't the most precise options available. And even though the Wii sold 100 million systems worldwide, a good majority of those sales came from casuals and non-gamers, who bought it for Wii Sports, Wii Fit, and other similar titles. Which meant more core gamer oriented titles often under preformed, and this affected how developers saw the console. 

The Switch by contrast has none of those issues. While its no Xbox One, the Switch is powerful enough that most PS4 and Xbox One content can be ported over with relative ease. Much like the DS, it's easy and low-cost to develop games for thanks to its Nvidia Chip-set and development tools, making it an especially attractive option for indie developers. It has a bunch of neat gimmicks and novelties, but unlike the Wii Remote, the Joy-Con also have the layout of a standard controller, which means they can act as a traditional controller when needed. And even more so than the Wii or DS, the Switch is appealing to a wide variety of consumers and gamers, who are buying a variety of different types of games for it. Not only are casual stuff like Just Dance and 1-2 Switch doing well, but so are Breath of the Wild, NBA 2k, Skyrim, Street Fighter, and a slew of indie titles. Switch owners are buying core games, lots of them, and that's encouraging to third parties. 

Point is, the Switch is in the best position to have Nintendo's most reliable third party support in years, despite being less powerful than the contemporaries. Now this doesn't mean every game will get ported over, there are obviously limits to what you can run on a tablet. But if third party sales keep up, we won't be missing as many games as you may think.