From a logic stand point why is this for 3DS for the time being:
- Larger user base at a more accesible price with the 3DS platform.
- Project was in development substantially before the Switch was out, maybe back to 2015?
- The Switch is still supply constrained and Nintendo expects this issues to continue even past hollyday season.
- There's nothing that prevents an eventual port happening for the Switch.
If you announce and release the game for both platforms at the same time there's the chance that the game's performance is trunkated on the 3DS and that it doesn't reach it's full sales potential on the Switch due to supply constraints.
And eventual port can totally be in the cards. And it makes sense to announce when it has had enough time to stretch it's legs on the 3DS and when the Switch reaches higher sales numbers. There's also the benefit that with extra time the potential Switch version to get some enhancements beyond doing the exact same game just in a higher resolution.