The reason this is not done is because of programming issues. No game is programmed being able to take on two (example) Requiems at the same time. In fact, I believe that if this were done that one Requiem would not go through due to it only being able to add the status to a character that is double.
Most of the code in the game disallows stacking certain things, and most things have a limit of 1, such as Requiem. Its more the serious programming challenge that makes this harder to put into place.
I agree it would be a neat feature. Don't know if they're going to put the time, effort, and money into making it happen.