The reason why cats' eyes glow at night is because they have a "fundus reflector" structure inside their eyes. This structure reflects the light that enters the eye, creating what we see as a "glow".
So, why do cats need such "glowing" eyes? This is because they are nocturnal animals. In the wild, cats are mainly nocturnal, looking for food and avoiding predators. In such an environment, cats need to have eyes that can see their prey clearly in the dark. And the "glowing" eyes meet this need.
In fact, not only cats, but many other animals have similar eye structures. For example, some animals such as snakes, birds, and insects also have such eye structures. This is because these animals also need to be able to see their surroundings clearly at night or in low-light environments.
Of course, our human eyes don't have such a structure, so we can't see the cat's "glowing" eyes. But if we can look at the cat's eyes, we can see the structure of the reflector, which is like a mirror, reflecting the light that enters the eye.
In short, cats' eyes are able to glow at night because of the reflector structure of their fundus, which reflects the light. This structure is the result of the cat's adaptation to nocturnal activities, and it is also an important guarantee for their survival and reproduction.