I agree with you OP but i would say :

-More mature consumers are the target compare to the Wii/DS/Wii U/3DS era (which doesn't mean kids and casual adult players won't jump in, kids like to feel mature anyway, look at call of duty lmao)

-Nintendo fans have only 1 system to buy. Might seem stupid, but once you don't have to buy 2 times a mario kart game for 2 different consoles, you have time and money for something else. I have so much more games on Switch than on my previous Nintendo consoles for that reason. I like having everything on the same device and makes me feel like buying games on it is worth it.

-I would also add the love for the system in general. People love the Switch a lot, it doesn't only sell well but people still like it a lot, which yes it's a big deal. You see so much more positive feedbacks online and it makes you want to spend money on it, from what i feel and i've read a lot on Twitter.

It's not only third party that sells more but also Nintendo games. Almost every entry on switch has been the best selling of it's franchise or will be in the future. Like even kirby that got rolled on by the press is passed like 2 million shipped. Games are just selling incredibly well on it that's all, but it's nice to see it not being limited to first party games tho.

Some games are just better when played on the Switch. I loved playing South Park 2 on my Switch, Crash is like meant to be played on the console, Skyrim is amazing on handheld, so is Doom, and I can't wait to play DB FighterZ on it.

Third party games have always sold pretty well on Nintendo handheld devices. That is why Nintendo handhelds always get good third party support.

They sell double because the other half of 3rd party games isn't on it. Simple math.

On first place I would said, because hybrid nature of Switch, game could be played in full handheld mode also and that gaves extra value to games.

I thought about it too and it was a riddle for me for some time. Because user-base isn't really much bigger than on WiiU yet, but still game sales are so much better. So I guessed, Switch attracted a different user-base than WiiU, that is more willing to buy games. And I asked myself, what different user-base that is.

But then I realized something. Early adopters are such, because they are interested in gaming and have money readily available (not have to wait until they got enough together). So they probably own multiple gaming devices they are interested in. That changes the question from 'Which user-base is more willing to buy games?' to 'On which platform the users want to buy their games?'. And that solved the riddle. There was basically no reason to prefer the WiiU-version of a game over some other version. This is differently with Switch.

Here are some reasons I think might influence people to choose one version over another:

• performance: If they own multiple platforms the game is releasing on, users might decide for the version the game looks or plays best. Advantage: PC and XBox One X
• online: On online centric games, the platform offering the best online experience might make the gaming experience so much better, that this is the version of choice. Advantage: PS4 and Xbox One (especially if the free game offers already drawn people into their online offerings)
• friends: If you want to play with your friends, you choose the platform you can play with them together. Advantage: PS4 or cross-play
• convienience: You might choose the version you have the least hassle to purchase, install and play. Advantage: Switch (short play sessions without firing up the TV, play in bed etc.) and generally consoles are more convenient than PC
  
• mobile: There is an advantage to take your game with you. Advantage: Switch

Obviously you must be drawn into a platform in the first place. But while both WiiU and Switch might have drawn gamers with the Nintendo-games, the WiiU offered no reason to purchase multiplatform titles on that platform. Switch does.
 

It's brilliant marketing and a concept that really entice people to buy games on it

Some people always seem to know a lot.

Wow thank you very much lol

starving for content. i know i am. so when something of interest comes along it is jumped on.

plus the ability to have it portable has a factor to do with it.