Pokemon Sword and Shield Were a Big Missed Opportunity for a New Eeveelution

gamerant.com:

Pokemon Sword and Shield sought to develop the traditions and expectations that the series set before it. For example, Sword and Shield continued the trend of regional variants, and it also established its own unique mechanics — chief among which being Dynamax and Gigantamax Pokemon, just as Mega Evolutions had been special for Gen 6 and Z-Moves for Gen 7.

While Sword and Shield were the latest entries in an extensive lineage that changed the Pokemon series' core gameplay, one tradition that fans anticipated but was never delivered is a new Eeveelution. Eevee and its many evolutions were not only included in Sword and Shield, but the base Pokemon even got its own Gigantimax form. Still, the games missed a major opportunity to introduce new Eeveelutions based on more unused typings.

Pokemon: Imagining What the Missing Eeveelutions Could Look Like

Ever since its introduction in Gen 1, Eevee has remained a fan-favorite Pokemon, not just for its adorable design but for its unique evolution versatility. While there were just three Eeveelutions at the start, as of this writing there are eight — accounting for nearly half of all available Pokemon types. When Eeveelutions are introduced, they often reflect a new element of gameplay, such as Umbreon and Espeon reflecting Gold and Silver's day-night cycles and X and Y introducing Sylveon alongside the new Fairy type.

Additions to the Eeveelution line come roughly every two generations, meaning fans were anticipating a new one to come with Generation 8's Sword and Shield. Yet Sword and Shield didn't have new Eeveelutions, and the reasons for this are speculative, but it could possibly be that with a Gigantamax form being given to Eevee, Game Freak decided to let that be the focus of