In 1e, specifically Inferno, they make the distinction that the Abyss can be viewed anti-reality and ultimately wants to annihilate the world, subsuming it piece by piece. Off-hand I don't recall if the Abyss is doing the same to the Lower Depths, but at least Inferno actually love (in-so-far as they are able) the world as it is. The Abyss is destroying what Inferno seeks to claim for its own, and there is a brief sidebar describing how the two realms occasionally clash in open battle. In short, the Abyss wants to devour what Inferno seeks to corrupt, and the two goals are mutually exclusive