In that game the frustration move is bc the badguys did some evil techno-magic to the mons that makes them angry and aggressive, and if you treat the shadow pokemon well it will "open their hearts" and they'll lose the frustration move. It exists bc the bad guys hurt the pokemon's feelings to weaponize their alienation.

And making them spirits isn't any better. Kami aren't any less individuals with feelings than animals or pocket monsters.