The whole point of this game is to get the feeling of being alone in a dense forest with a paranormal creature stalking you. You're supposed to feel scared because you have nobody to protect you. With another player you feel safer and therefore, makes the game less scary
That's how it may sound on paper, but have you actually played a multiplayer horror game (that was actually scary)?
Chances are, there may be parts in the game where players have to split up, or maybe they will start in different locations. Nonetheless, a multiplayer horror game can still be just as scary as singleplayer.