why manga outsells comics

How could I forget? The infamous lesbian orgy is actually very thematically important to the story of Chainsaw Man.

Chainsaw Man is a manga about (among other things) how indulgence in base urges can actually lead us away from the things that would make us happy in the long run. Quanxi adds to this theme by frequently indulging in lesbian orgies and telling Kishibe that she'd rather continue to do that than fight Makima, because "ignorance is bliss." …and then Makima kills her and everyone she loves. This is a pretty direct parallel to what happens to Denji, which is why the fact that Quanxi also directly tells Denji that "ignorance is bliss" is significant. The arc ends with Denji coming to the same conclusion about ignorance, deciding he knows too much about Power to be attracted to her. But then, in the very next arc, Makima kills Aki, then kicks off the next arc by killing Power, showing that Denji's willful ignorance about how Makima was manipulating him for the sake of (he hoped) eventually sleeping with her has actually destroyed his life. Having seen the brutality of the world, both him and Quanxi decide that the pursuit of carnal desires is just as valid a goal as any other …but their chosen ignorance ends up ruining them in the end. (Which is also why Denji loses his "dream battle" early in the manga).

So yeah, I'd say the lesbian orgy is actually a pretty important thematic addition to the story.