How come you cannot trade an Enigma Berry from Pokemon Emerald or Ruby to Pokemon Sapphire?

Because Enigma Berries are like a Willy Wonka Gold Ticket. Once you get it you really don't want to give it away. you sapphire game need an BERRY UPGRADE then you can trade it

- when you get ur emerlad and sapphire link up, turn ur emerald on and wait until the screen with the press start appear on it the press b, down, and select and follow the instructions