Because people search, judge and decide which games they play based on the tags. If a game has the tag 'rape', some people might think: "Nice, a game with dark content like that", others: "If it has that content, then I'll never play it". Here, the game's main aim is to provide a good atmosphere and a wholesome feel, so the devs don't want to present this kind of tag.
The same goes for "Kinetic Novel", I think most people have a negative opinion of this tag, hence the presence of choices in the game, important or not.