As a very crude analogy think of a rubber sheet with a heavy ball placed in the middle. Replace this heavy ball with a pile of sand, where the sand is most concentrated the sheet is depressed the deepest. As you spread the sand across the sheet the depression becomes shallower until once spread evenly across the whole sheet the depression disappears. I guess you could say that energy works in a similar way. In the universe very dense lumps of energy form matter, as this congregates to larger lumps the curvature of space becomes more apparent. As you know very massive objects concentrated in a very small volume curve space-time to such an extreme that even light cannot escape, hence the existence of BH's. Spread this energy/matter over a large area the effects of curvature become less apparent.