EDIT: This is probably due to jazz musicians taking themselves more seriously and wanting to be known more for their music than anything else. If a jazz artist enlisted Dir En Grey's stylist, it may invite insinuations that any success is due to marketing instead of artistic merit.
EDIT: To further clarify -- average person's image of:
Rock/Metal: shirtless guys with long hair and tattoos playing guitars
Pop: Pretty boys/girls in shiny costumes who can dance
Jazz: dude with curly hair holding a saxophone