Why is it said that sunlight provides energy either directly or indirectly to all living things on earth?

Because the sun provides not only provides for living things, it provides for some indirectly because the sun is everywhere. That being said, a good example would be the grass. And what eats the grass? Animals and critters of course. Sun also makes trees grow which gives us humans oxygen. The sun helps us in many ways whether you know it or not.

Because in order for plants to grow, we need sunlight. And the animals that eat the plants will be eaten by other animals, until finally we humans eat the animals. So even if you aren’t directly eating the plants, the animal we ate needed the plants to exist, therefore, needing the sun to exist.