Space appears dark to us because it is primarily a vacuum, devoid of significant amounts of matter to scatter or reflect light. The Sun's light illuminates the Earth because it is relatively close to us, and the Earth's atmosphere scatters and diffuses sunlight, making the sky appear bright during the day.
When we look out into space beyond our atmosphere, we encounter vast distances with very little matter to interact with light. In the absence of any significant light sources nearby, space appears dark. There are some faint sources of light in space, such as distant stars and galaxies, but they are often too dim or far away to be visible without the aid of telescopes.
It's worth noting that even though space appears dark to the human eye, it is not completely devoid of light. There is a low level of background radiation present throughout the universe, known as cosmic microwave background radiation, which is a remnant of the early stages of the universe. However, this radiation is not visible to our eyes without specialized equipment.