Why is it necessary to have a constant input of energy into an ecosystem?

If there was not a constant Input of energy into the ecosystem then nothing would have the power to do anything and nothing would be alive. the energy starts with the sun, then goes to plants, then animals that eat the plants, and then the animals that eat those animals, Ect. if this chain reaction did not happen then the plants wouldn't have to power to go through photosynthesis and then we would get no energy. the amount of energy lessen with every chain that it goes through, this is why we get more energy eating plants and why they are healthier.