"Porn addiction" and "sex addiction", by themselves, are folk diagnosis. Compulsive behaviour around sexuality may happen same as anything else, but there is no primary diagnosis for it in the DSM-V for the same reason homosexuality isn't in there.

Further, it tends to be a Trojan horse for Kellogg-esque ideas about sexual purity and to scapegoat sexworkers. Finally, since "porn" can be defined any way a person likes, sex-ed materials & queer narratives are targeted.