You missing another huge issue. The (3)DS's dual/touch screen capabilities are a unique concept that has given birth to several franchises both first and third party. The switch cannot emulate the effect of using two screens at the same time the same way the DS's could Nintendo would be stupid to drop it in favor of the switch.

Third, and more importantly, not everybody owns a Nintendo Switch.
It's a new console, they're expensive (especially outside the US, where I live a Switch costs over $ 750 dollars), they're hard to get, there are not enough in existence. (Nintendo right now is having a hard time trying to get manufacturing parts)

The 3DS family, on the other hand, is more accesible (with the 2DS being cheaper) and it's more likely that people already own it.

And if people that don't own a Switch, and would buy it until a Pokémon game is announced, That means that they're not really interested in the Switch .