Why do consumers depend on producers? Why do producers need decomposers?

Firstly, producers get their energy energy from the sun through photosynthesis, creating or producing nutrients in the plant. A herbivore consumer can then eat it getting it's nutrients so, consumers rely on producers for their food but decomposers rely on a carnivore or omnivore (consumer) to eat some species of a consumer. The decomposer, lets say a earth worm eats and consumes the rest of the animal breaking it down to it's core nutrients. So I guess you could say decomposers rely on carnivores/omnivores to kill each other and herbivores, and herbivores/omnivores rely on producers for nutrients to eat