>In Gen IV you need to have all the elemental titans in your party to catch Regigigas
>You need to have Regigigas in your party to catch the elemental titans
Why is this allowed?
Not just any Regigigas, a limited time event Regigigas that only works in platinum
>>27809622
You transferred the regis from RSE to get Regigigas in DPPt. It ties very well into the lore from Hoenn.
Getting the regis in HGSS afterwards is entirely different, it wouldn't matter if the DPPt Regigigas was easily accessible since you needed a special event Regigigas.
Did you even play the game?
[spoilers]Gamefreak[/spoilers]