An inquiry on Eevee's addition to Pokémon Champions

Hello Pokémon Company. I have a simple question. Why isn't Eevee part of the Pokémon Champions roster of playable Pokémon, while Pikachu is? Isn't Eevee considered the secondary mascot of the Pokémon Company alongside Pikachu? Isn't that why you created Let's Go Eevee alongside Let's Go Pikachu, because you consider Eevee the secondary mascot?