Kuiper belt objects are actually comet nuclei. why do they not display coma and tails

Though Kuiper belt objects are actually comet nuclei, they do not display comet tails because those develop the closer the comet gets to the sun. The coma, an area of vaporized gas around the nucleus of a comet, also develops as the comet gets close to the sun and it's ice begins to vaporize. Since the Kuiper belt is so far from the sun, the tails and coma are not displayed.