Factor Number 1
Nintendo has been around a long time and there is more of a nostalgia fact which has lead to more of a collectors culture around their titles.
Factor Number 2
Most (not all) Nintendo first party games are designed and marketed to be ever green titles. If you're buying a Switch 4 years after the system came out and you look at the library of games for sales I don't see there being a big difference between Mario Kart 8, Smash Bros Ultimate, or some newer game. They are all essential games for a library. Whereas with 3rd party games there's a huge difference in perceived value in Madden 18 vs Madden 2023. One has an outdated roster and no online community and one has a current community and roster. 3rd party games more often than not are designed to become obsolete but Nintendo first party games are designed to be relevant for the life of the console.
