Pokemon Sword and Pokemon Shield may not have added any new Eevee evolutions, but at least they brought back all of Eevee's past evolutions. It wouldn't be the same Pokemon experience without Vaporeon, Flareon, Leafeon, and all of the other Eevee evolution types. But even Eevee's evolutions didn't fully escape Game Freak's changes in Pokemon Sword and Shield. Both Leafeon and Glaceon reportedly have new ways of triggering their evolutions in the new Nintendo Switch games.
For Eevee enthusiasts, don't worry too much about the change. If anything, it's going to make evolving Eevee into either Leafeon or Glaceon in Pokemon Sword and Shield much simpler than in recent Pokemon games. Those with past Eevee experience will recall that, in order to evolve Eevee into either Leafeon or Glaceon, players must have either the Moss Rock or Ice Rock, respectively. Since these are items with little use, they're often very rare. So in Pokemon Sword and Shield, Game Freak removed them from the game.
In order to evolve Eevee to either Leafeon or Glaceon, Pokemon trainers now must have either a Leaf Stone or an Ice Stone. These are already existing items that previously caused the evolution of several other Pokemon, just not Leafeon or Glaceon. The exact reason for Leafeon and Glaceon having more unique items for their evolution isn't entirely clear, but it won't matter going forward.
Pokemon Sword and Shield players will find Leaf Stones and Ice Stones surprisingly common in either game. Just being attentive while exploring Pokemon Sword and Shield's routes should produce a few stones found on the ground. They can also be found in the Wild Area, like so many other random items. The point is that they're widely available starting early in the game, rather than be a challenge to find until endgame.
The changes to Leafeon and Glaceon's evolution from Eevee are just the latest example of Game Freak's overall strategy of adjusting aspects of the Pokemon franchise where it makes sense. For example, turning on EXP share for a trainer's entire party made sense, since the vast majority of Pokemon players already used it. With Pokemon games being released every one or two years, there's only so much that can be done, but Game Freak does optimize the experience as it's able.
Pokemon Sword and Pokemon Shield are available now on Nintendo Switch.