If Nintendo wants to launch next-gen hardware, then they have games for it. And if they want to show those games during/after the hardware is announced, there is going to be a fallow period before that launch.
We've been living with a cross-gen period in our mind for so many years, but Nintendo is about to have a proper 6.5/7 year Switch generation. There is every reason to hold games till after announcement, rather than announce games, then say they'll be playable on new hardware. The better marketing move, even if they are cross gen, is to show the games in full glory on day one, then mention they'll be playable on your old Switch (in 720p graininess).