Because it’s not a message plus an entirely separate mechanical system
Except they kinda are separate. It doesn’t matter how good your story is, if it’s a total slog of mediocre boring gameplay to get that story I’m just not gonna bother. If the actual game part of your game is bad, it’s a bad game; if only the story is good, you may as well make it a movie,book or something else like that.
Telltale games were also really bad games for basically the same reasons, should’ve just been direct-to-video/streaming movies. Fight me.