Also, reminds me of this.

I can certainly relate to not noticing errors in a long post. At least errors like that are funny! For the topic itself it seems obvious to me that of course the primary driver of what's gonna be the 2nd or 1st best selling Nintendo system ever are people who owned the current top 2 Nintendo systems. I could go into detail but you've already explained it better than I possibly could.

Nice idea.
I'd put Intellivision and ColecoVision in "Arcade Evolution" category, their controllers with numpad allowed more and more complex actions than in most typical arcade games, and you could insert overlays (most Intellivision ones included them) on the numpad to map it to game specific actions, both consoles offered expansion that made them even more complex than typical arcade consoles and Intellivision had a controller suitable to more complex controls, but less suitable to the most frantic arcade games, due to position, size and stiffness of its main buttons.

It's weird. Besides Wii Sports, Switch has literally everything that was successful on the Wii in terms of hardware and software. So, I think the question is why wouldn't the Switch appeal to that audience? Unless you think Wii Sports was literally the only reason thing people liked about the Wii, then there's really no good answer.

PS fans are finally upgrading to a Nintendo system. You pointed out that Switch doesn't have any PS/MS games. It's also true that PS/MS don't have many 'Nintendo' games. The only logical explanation is that Sony/MS fans have finally realised what they've been missing out on all these years and have decided to make the jump.

It's a chicken and egg situation. There's a lot of people who don't realise that Wii Sports is exactly the sort of game the Nintendo-core likes.

People act like Wii Sports was a new direction for Nintendo, but it really wasn't out of the blue. Mario Kart, Mario Party, Smash, Kirby Dreamland/Air Ride, Mario Sports, Animal Crossing etc. were all efforts to make accessible games. The Wii was just the point where they went the furthest towards simplicity, simplified the user interface, and put it at the forefront.

It's an extension of what they'd been doing, and it's not hard to see why there'd be a big overlap between Wii Sports fans and Mario Kart fans.

Seems legit.

It wouldn't appeal much to the crowd that only bought it for Wii Sports but that crowd isn't that big considering how well games like Mario Kart and New Super Mario Bros did. It certainly isn't a coincidence that Mario Kart 8 DX is the best selling Mario Kart game since the Wii one. A lot of people who bought the former will have played the latter as either a kid or young adult.

I think the "mainly/only bought it for Wii Sports/Fit" crowd is substantial, but the question of why the person bought the Wii is largely irrelevant to whether or not they would buy a Switch. The more apt question is what did they enjoy on the Wii.

Just because someone got caught in the Wii Sports craze and bought a Wii doesn't meant that's all they played on the Wii. Wii Sports was basically a trojan horse. Nintendo obviously didn't plan to sell a Wii to someone for a minor profit and never make another dime off of them. The hope obviously was that they would buy Wii Sports and then would go on to buy other games. And since sales of basically every Nintendo franchise went up, it seems like that's exactly what happened. And quite possibly they liked these games enough that in the future their sequels might help influence them to buy a new system.

Again, it really comes down to the fact that from the beginning some people hated the Wii and were arguing that the people buying it were filthy casual gamers who would lead to Nintendo's downfall in the long run. And they're sticking to the narrative regardless of whether there's any evidence.

To be more clear I meant people who bought a Wii for Wii Sports and then after growing tired of that game barely used the Wii anymore. The crowd who bought a Wii due to games like that and then went on to buy other games like Mario ones is far bigger so I agree with your analysis. Some of the Wii's success did come from people who only ever played stuff like Wii Sports but the size of that group is often quite overstated.