Why do pillow fairy tales sound a little melancholy?

Artistic conception of lyrics. The song "Fairy Tales by Pillow" has a light and sweet melody and an indescribable feeling of love and sadness. Moonlight tells the plants outside the window to remember to give way when meeting children. Who will save my loneliness? You are a princess in a fairy tale standing in the light. These lyrics say that there is no princess or prince in the world, but everyone will have a beautiful princess or prince in their hearts, and also write the sadness that adults want beautiful love but can't love it.