https://wccftech.com/pokemon-never-features-full-pokedex-again/

As you may have heard, there’s a bit of controversy surrounding the upcoming Pokemon Sword and Shield, specifically regarding its limited Pokedex. While you can only catch a select number of critters in each new Pokemon RPG, there have always been ways to import your past favorites into the latest game once you’d finished the main campaign. That’s no longer the case, and according to long-time Pokemon overseer Junichi Masuda the option probably won’t be returning (thanks to VG24/7 for the translation)...

We currently have no plans to make the Pokemon that are missing from the Galar [Sword and Shield] Pokedex available in-game. This is an approach that we want to continue with in future Pokemon games.