Here's why:

* Fungi: They break down dead organic matter (like leaves, wood, and animal carcasses) using enzymes. This releases nutrients back into the soil, making them available for plants.

* Bacteria: They are even more diverse than fungi and can break down a wide variety of organic materials, including cellulose, proteins, and fats. They also play a crucial role in nitrogen fixation, a process that makes nitrogen available to plants.

While other organisms contribute to decomposition (like earthworms, insects, and some animals), fungi and bacteria are the primary decomposers, responsible for the essential process of breaking down dead matter and recycling nutrients within ecosystems.