Because "that" jutsu was most likely just utilizing the kyuubi cloak/tails...last time naruto used it during the timeskip, he almost killed jiraya... which is why when jiraya mentioned it , naruto said "I know" with a depressed look..
is one that Naruto needs practice on a girl with,
and he and hinata cant practice (that) brand new kage-bunshin technique right now - as they are in war.