I think it just comes down to the game being not very good. It's not really designed for retention. Once you've caught the Pokemons you care about, there's no

I think it just comes down to the game being not very good. It's not really designed for retention. Once you've caught the Pokemons you care about, there's not much left to do. Gyms are not an interesting mechanic, and there's no other way to interact with other players in the game. Basically, Niantic put out a half-baked game, which was rapidly successful only because it built on the combination of a fantastic idea (AR gaming) and a cherished IP (Pokemon).