its probably because the person your trading with has not yet beaten the Pokemon league. When he/she does this, you can trade away!
hope i helped
~MetalUmbreon
You cannot get a Yanma in Pokemon Emerald, as only Hoenn Region Pokemon can be found in Pokemon Emerald.
you cannot get groudon in emerald
No you cannot catch Entei in Pokemon Emerald.
You cannot get Rhyperior in Pokemon emerald as he is only in Pokemon diamond and pearl.
The Growlithe cannot be found in Pokemon Emerald but you can trade it fromPokemonFirered.growlithe cannot be caught in emerald, Sapphire or ruby. it must be traded from fire red
You cannot get a Yanma in Pokemon Emerald, as only Hoenn Region Pokemon can be found in Pokemon Emerald.
you cannot get groudon in emerald
No you cannot catch Entei in Pokemon Emerald.
You cannot get Rhyperior in Pokemon emerald as he is only in Pokemon diamond and pearl.
You cannot get Regigigas on Emerald version.
No, players cannot get a Dobby for the Pokemon Emerald version of the game. Pokemon Emerald released in the United States in 2005.
The Growlithe cannot be found in Pokemon Emerald but you can trade it fromPokemonFirered.growlithe cannot be caught in emerald, Sapphire or ruby. it must be traded from fire red
You cannot keep a pet Pokemon in Pokemon Emerald. Pokemon are considered your friends, and as such are placed in your party and cannot be kept as recognized pets in the game.
No you cannot catch Celebi in Pokemon Emerald.
You cannot find an infernape in Pokemon emerald for that Pokemon you need Pokemon platinum, pearl or diamond.
You cannot get the Dawn Stone in Pokemon Emerald, as it is first introduced in Pokemon Diamond and Pearl
Pokemon Emerald takes place in a different region than Kanto (the home of Pallet Town). You cannot go there in Pokemon Emerald.