I'm The One That Took Your Rug

Also sometimes the purpose of a sex scene is to be titillating and that's, like, fine. You wouldn't go out there and argue that movies shouldn't have jokes unless they "serve a narrative purpose" because you understand that generally the purpose of a joke is to make the audience laugh and perhaps release some tension. Being horny is a normal human emotion like being amused or being scared and sometimes media is trying to evoke that particular emotion; the artist doesn't owe you a 30-page double-spaced justification for trying to make you feel something through their art. Your separation of horniness and sex from other emotions and experiences is sex negative and deeply ingrained in cultural conservatism.