In SwSh there couldn't be the file datas of every specie of the previous generations, also for several "banal" reasons I am going to show below
Have you ever thought... When Rockruff rises to level 25, it evolves into Lycanroc, depending on the game:
il will evolve into Lycanroc Midday Form in Sun and UltraSun during the day, and similarly it will evolve into Lycanroc Midnight Form in Moon and UltraMoon during the night: but in Sword and Shield, that are not Sun neither Moon, UltraSun nor UltraMoon, in which form of Lycanroc it would evolve into reached level 25???
With Cosmoem the same: reached level 53 it evolves into Solgaleo in Sun and UltraSun, instead into Lunala in Moon and UltraMoon: but in Sword and Shield, or in any next game that is not settled in Alola, who will Cosmoem evolve into?
And Meltan and Melmetal? They don't have the ability, neither the evolution method of Meltan can be supported in any game of the main serie, because it involves the candies of Go, absent in every game of the main serie.
And Oricorio? It is a Pokémon based on the Alola region that changes its first type depending on the island you are (for wild Oricorio), or using Nectars (for trainers' one), but both are based on Alola, it'd be absurd having Nectars in other regions, such as color-based locations where to find different form of the bird.
So Rockruff-Lycanroc, Cosmog-Cosmoem-Solgaleo/Lunala, Meltan-Melmetal and Oricorio can't be in SwSh; I'm not going to state that this is the main reason for having the file datas limited only to the species of Galar Pokédex, but this is a sufficient condition for which there can't be the datas of all species of Pokémon, from Bulbasaur to Melmetal.
Have you ever thought... When Rockruff rises to level 25, it evolves into Lycanroc, depending on the game:
il will evolve into Lycanroc Midday Form in Sun and UltraSun during the day, and similarly it will evolve into Lycanroc Midnight Form in Moon and UltraMoon during the night: but in Sword and Shield, that are not Sun neither Moon, UltraSun nor UltraMoon, in which form of Lycanroc it would evolve into reached level 25???
With Cosmoem the same: reached level 53 it evolves into Solgaleo in Sun and UltraSun, instead into Lunala in Moon and UltraMoon: but in Sword and Shield, or in any next game that is not settled in Alola, who will Cosmoem evolve into?
And Meltan and Melmetal? They don't have the ability, neither the evolution method of Meltan can be supported in any game of the main serie, because it involves the candies of Go, absent in every game of the main serie.
And Oricorio? It is a Pokémon based on the Alola region that changes its first type depending on the island you are (for wild Oricorio), or using Nectars (for trainers' one), but both are based on Alola, it'd be absurd having Nectars in other regions, such as color-based locations where to find different form of the bird.
So Rockruff-Lycanroc, Cosmog-Cosmoem-Solgaleo/Lunala, Meltan-Melmetal and Oricorio can't be in SwSh; I'm not going to state that this is the main reason for having the file datas limited only to the species of Galar Pokédex, but this is a sufficient condition for which there can't be the datas of all species of Pokémon, from Bulbasaur to Melmetal.