Why cant you go to black city in Pokemon Black 2?

In Pokémon Black 2, players cannot access Black City if they are playing Pokémon White 2. Black City is exclusive to Pokémon Black 2, while White Forest is its counterpart in Pokémon White 2. The game mechanics tie these locations to the version you are playing, meaning each version has unique areas and Pokémon that reflect its theme. Thus, only players of Black 2 can visit Black City.