After you beat the Elite Four and the champion in Let's Go Eevee, there is a Sandshrew master but you can only get Sandshrew in Let's Go Pikachu. So why is there a Sandshrew Master in the game?
The Pokemon may be version exclusive, but the Master Trainers are not. You could trade with someone with Let's Go Pikachu if you want a Sandshrew (though practically no one is playing that game nowadays).
