>>51864392Because there's literally only two Fairy type moves, and they only added the second a few months ago.
You know what Fairy type moves Xerneas learns that aren't already featured?
Misty Terrain, and Geomancy.
That's it, both status moves.
Geomancy being its signature move can conceivably be implemented as a high-energy low-damage charge move with PvP effects of sharply raising attack and defense.
Misty Terrain does not make sense as as fast or charge move.
This has been an ongoing problem for Go, it relies on the movepool of each new generation to fix these problems.
Especially with legendary Pokémon not learning low power moves which are adapted as Fast moves.