Probably because a fixed seed is also more resource-consuming. For all intents and purposes a container is dead to the game as long as it's unopened. Only when it is, it will become a part of savegame content. And it can be completely wiped if there's a path of no return (though I am not sure if Original Sin will be like that). With a seed like yours ALL containers will need to be logged from the start. Increasing loading times, saving times, savegame space usage, etc.
And as you already mentioned yourself... there will be other exploits replacing this too. One way or the other people will.
