Why is the background of the universe black?

It's like the night on the earth, and the stars in the starry sky are not enough to illuminate the night. At this time, if there is a lighted candle, the light of the candle can only illuminate a small area, and the place where the candle can't shine is still dark. The celestial bodies in the universe are stars except planets. Planets don't shine. Stars can emit light and illuminate neighboring planets, but their light is limited. Even if there are 20 trillion to 40 trillion stars in the universe, even if all these stars are arranged in a matrix, they can only illuminate the surroundings like candles lit at night, but the candle illuminates a much wider range. Even so, because the universe is too big, it is beyond the irradiation range of this matrix. In fact, it is impossible for stars in the universe to form such a matrix. Stars spread out to form their own small galaxies, just like the solar system. Every galaxy is far away, and the places where the stars can't shine are all black.