>>29209122Because they don't have "muh deep spiritual connection" and can easily be placed in the care of Oak. The dug a hole when they made Greninja as important to Ash as Pikachu is.
Releasing was the only option because if he dropped him off with Oak he'd be considered no more important to the story than Tauros and if he took him to Alola he'd be an overpowered monster or he'd suffer from Unova Syndrome.
