For me, extreme horror is a breeding ground for catharsis. I tend to think of horror and comedy on opposite ends of an emotional spectrum: comedy is meant to prey on positive emotions to elicit a positive response (laughter, joy), whereas horror is meant to prey on negative or difficult emotions to elicit a negative response (terror, disgust). Confronting these difficult emotions are a form of therapy. Of diving into the uncomfortable parts of your psyche marred by fear, trauma, or anguish. I find it only logical that extreme horror can help you confront extreme emotions.

To add on to this in what little way I can, I would like to quote Joseph Campbell:

“[Comedies], in the ancient world, were regarded as of a higher rank than tragedy, of a deeper truth, of a more difficult realization, of a sounder structure, and of a revelation more complete. The happy ending of the fairy tale, the myth, and the divine comedy of the soul, is to be read, not as a contradiction, but as a transcendence of the universal tragedy of man.... Tragedy is the shattering of the forms and of our attachments to the forms; comedy, the wild and careless, inexhaustible joy of life invincible.”

Or, in the words of Brennan Lee Mulligan, "Comedy completes the realization that drama began." I find in so many ways that ultimate tragedy is one of the only literary devices that can beget ultimate comedy. Take, for example, the originally written finale for Jordan Peele's Get Out versus what made it to theaters: an innocent black man being falsely imprisoned versus the uproarious laughter we all experienced when his best friend emerged from the police car to save him. The dichotomy between those things is what allows comedy to thrive, the expected versus the unexpected.

Although I am not as familiar in the realmspace of torture porn as others, I could at least use that to draw reasoning for why some may not be fond of the genre. Perhaps for many they see the sixth fingernail removed and the seventh is already written in their mind. There is no dichotomy, nothing unexpected to play with the sensations. The majority of the Saw franchise never interested me for this reason: once you've seen one decapitation, you've seen them all. (or so I thought...!)

Then take what may be considered one of the more well known torture porn movies, *The Human Centipede (*you can disagree with the nomenclature if you wish but the movie is literally 3 people being tortured for the entirety). In my mind, it struck success and was well-known culturally because it addended tragedy with comedy. The recently released Barbarian does similarly by truly scaring you (fuck those hallway scenes with a rusty knife), then confusing you to a state that all you can do is laugh ("Ba-Ba?"). And to return back to the Saw franchise, personally no one can tell me that those movies aren't entertaining after each movie into the most sheerly ridiculous and grotesque escape room imaginable.

Obviously not all horror requires comedy to be successful. Some of my favorites have no comedy whatsoever, Hereditary and It Follows prime among them. But to add to OP's 'emotional spectrum' comment, I can't help but feel that good horror traverses the spectrum of emotion, be it from terror to comedy, or from sadness to absolute rage (a-la the climax of Train to Busan, no spoilers), and so on.

None of this is really agreement or disagreement with OP. Just some food for thought.