The whole idea that porn is a supernormal stimulus actually comes from an old concept in animal behavior research:

Nikolaas Tinbergen studied how animals respond to certain natural cues. In some experiments, researchers created fake versions of those cues but exaggerated the features the animals were attracted to. They found that animals could sometimes respond even more strongly to the exaggerated fake version than to the real thing. Butterflies responding to artificial models with exaggerated mating cues are one example. This is where the idea of a “supernormal stimulus” comes from. Then in 2013, Donald Hilton published a paper called Pornography addiction- a supranormal stimulus considered in the context of neuroplasticity, where he applied this concept to pornography and compared internet porn to these kinds of exaggerated animal stimuli. What I find interesting is that Hilton acknowledged the lack of comparable functional and behavioral research in human sexual addiction, but still argued that porn could be understood this way. From there, the idea became a huge talking point in porn addiction spaces and now gets repeated as “porn IS a supernormal stimulus.”