It is not that simple even if it is a SP game. For some people, they want their Achievements to meant something, so it will bug the hell of them when they know other players will abuse the game to easily gaining Achievements. Some people can't control their urges of knowing, and it will always be on the back of their head while they playing the game. They try so hard to not do it, it will drive them crazy to the point of stop playing the game.