https://www.gamespot.com/articles/pokemon-for-switch-is-helped-by-ultra-sun-and-moon/1100-6454169/

Elsewhere in our interview, Game Freak explained why Pokemon Ultra Sun and Moon aren't coming to Nintendo Switch and stated which of the two games you should buy. Look out for more from the interview soon. The games, meanwhile, launch for 3DS on November 17, featuring an "alternate" story and some new Pokemon. If you're still playing the base games, however, you can check out all the free Pokemon and items you can get in Pokemon Sun and Moon right now.