It makes sense for Legends Z-A to decline from Arceus. A console's software selling potential naturally declines with age, it usually peaks at the midpoint of the system's lifespan and then gradually declines, and that decline should be pretty high for the Switch 1 now that its nearing 9 years old.
And Switch 2 is a new system that has yet to grow its user base enough to offset the big decline of the Switch 1 active user base as of yet.
Due to Nintendo consoles following the traditional console model with a focus of traditional games and not GAAS, it means it will follow the same pattern as all historical consoles. The reason why PS4 and Xbox one are still relevant is because of stuff like CoD and EA Sports games and other live service releases. While Switch 1 will behave more like Wii, Gamecube, N64 and other systems that would decline fairly hard and fast in software sales after they got replaced.
You won't see many people still playing Switch 1 in 5 years time like you see many people still playing PS4 and Xbox one today for that same reason.
