Should be a given that the vast majority of Switch owners has more third party games than Nintendo games over time; it's only in the beginning that first party games are in the majority because those usually happen to be the reason to purchase the console in the first place (e.g. 1-3 games bought with the console, of which 1-3 are Nintendo titles). While AAA third party publishers have a habit of botching their releases, indies have been a lot more reliable, so gamers are less hesitant to buy their games.
It's the same as it has always been: More quality in the third party support results in more sales for third party software. Regardless, "how big is the share of third party games in your collection" has been a reoccuring topic on gaming forums because detractors have kept putting the cart in front of the horse, framing the premise as if Nintendo console owners do not want to buy third party software when it has always been a question of quality.
11 of my 32 boxed games are Nintendo titles. Under 10 of my 50+ digital games are Nintendo properties.
Legend11 correctly predicted that GTA IV (360+PS3) would outsell SSBB. I was wrong.
A Biased Review Reloaded / Open Your Eyes / Switch Shipments