Why do domestic cats eat mice?

Mice are mammals and small rodents. The primary prey of the domestic cat are small mammals, mainly rodents. The domestic cat eats a wide variety of foods; from food that we provide, usually commercial cat food to birds, small rabbits, hares and rodents other than mice.

Birds, despite what many people say, are not a primary prey of the domestic cat. The domestic cat usually hunts on the ground as it is easier and it provides a stable basis or footing for the attack and kill.

On the ground the prey that a domestic cat is most likely to encounter is a mouse in may parts of the world perhaps because they migrate towards people's homes.

They also eat chipmunks in the USA. Norway rats can be too big and too aggressive for the cat but are still hunted and taken by the domestic cat.

In equatorial islands, the lizard is part of the domestic cat diet.

The mouse contains all the nutrients that are required by the domestic cat. It could be argued that the mouse is a model diet for the cat from which all domestic cat diets should originate.

Commercial cat food often misses the mark badly. See for example best dry cat food.