Because Dark Elements really have no place in a King's Quest game. Not to the extent at which QFGIV had them. It's a cheap gimmick used these days to make a game "more mature". People have been trying to shoe-horn darker elements on to KQ's with mixed results for a long time.
A "dark" King's Quest... isn't King's Quest. As I've said before, why do you want something new with an old name on it?