Because they lack chlorophyll (a green pigment in plants that helps them trap sunlight, used to manufacture their food through photosynthesis)
Explanation:
Mushrooms are heterotrophs. They are not plants or autotrophs. Mushrooms, just like every living thing that exists need energy in order to live. Only plants, or autotrophs, can directly use energy from the sun (the ultimate energy) to make food. Those organisms that cannot harness the sun's energy are known as heterotrophs. Mushrooms are fungi (belong to kingdom Fungi) and are heterotrophs because they decompose and consume nutrients from the soil. They are not green so they cannot photosynthesis due to lack of chlorophyll.
