Why don't gases keep their volume?

Gases do not keep their volume because their molecules are in constant motion and are much farther apart compared to liquids and solids. This high kinetic energy allows gas molecules to expand and fill the entire container they are in, regardless of its size. Unlike solids and liquids, which have defined shapes and volumes due to strong intermolecular forces, gases lack these forces, leading to their ability to change volume based on the container.