Obviously third parties sell a ton of games on Nintendo when Nintendo systems sell well.
It's just that third parties generally don't put their new AAA games on Nintendo these days so the mega selling games are all first party. But there's tons of indie and third party games that sell well, just not like 10-20 million.
But you can blame third parties for this. Nintendo is the best game maker in the world, so for third parties to compete with all the first party mega sellers on Nintendo, they'd have to actually bring their new AAA games to Nintendo's systems, but they don't. When it comes to AAA third party games Nintendo pretty much gets either last gen ports, two gens ago ports / remasters, or current gen games that are 6 months late or a year late or two years late so those games can't possibly compete with the sales they had when they were brand new.
I'd say for $60 games, people mostly buy first party on Nintendo simply because those are the best games on the system and are only on Nintendo and are brand new instead of being launched as an afterthought after the other versions. But the <$60 range, and specifically probably the <$40 range, is where third parties absolutely flourish on Nintendo.
I have 55-60 Switch games. I think ~24 of them are first party, most of those cost $60, though some I got on sale. Which means I have >30 third party games, probably none of which were $60 are were mostly $10 - $20 dollars, and probably most of those I bought on sale. So majority of my games are third party, but I have a lot of the 10/20/30+ million selling first party games.
