The answer would likely be along the lines of torches using a minimal amount of memory, while combat would involve adding multiple large sprites for the player in combat as well as many large sprites for the the combatants's combat and motion. Given that the game was already pushing the limits of computer graphics with it's art style, it was likely desirable to differentiate the appearance of at least some of the combatants, pushing the memory requirements even higher.
Then there was the author's lack of desire to make another game focused upon combat.
Which is the beauty of the shadow character. Since it is based upon a computational trick, it added a minimum to the resources required. At the same time, it afforded a twist in the plot that allowed the author to accept and integrate combat into the game. It changed the nature of the combat and of the player's decisions, permitted the antagonist to exist long enough to have it's own story, and got rid of the cheap feeling of a clone army (i.e. reused sprites).
Then there was the author's lack of desire to make another game focused upon combat.
Which is the beauty of the shadow character. Since it is based upon a computational trick, it added a minimum to the resources required. At the same time, it afforded a twist in the plot that allowed the author to accept and integrate combat into the game. It changed the nature of the combat and of the player's decisions, permitted the antagonist to exist long enough to have it's own story, and got rid of the cheap feeling of a clone army (i.e. reused sprites).