I am confused as to why this game is perceived by me to be a better story-driven game than most non-nsfw AAA games on Steam.
The clue is in what you wrote... "AAA games".
"AAA Game" as a term used to be something meaningful, that gamers hoped studios would aspire to in terms of quality. It quickly became a joke, then a distorted reflection of what it used to be, becoming a thing to avoid until it was half price or less.
Maybe it is just because I am more motivated to read the story with a lot of porn in it. However, I have fully read and played some games ( like Starfield, Spiderman, Control) and I don't enjoy them as much as I did with Superhuman.
Starfield doesn't really have a story.
It's a standard Bethesda snore-fest with "over-lore" to make up for lack of interesting characters and story, and managed to be the most boring and least interesting of all Bethesda Studios games to date.
On the upside, it was their most stable and bug-free release.
Not going to comment on Spiderman because I've honestly no idea which game you're referring to.
Control looked as boring as Quantum Break, so didn't touch it.
Another speculation I have is that sexual tension is an inseparable part of the human psyche; where it enhances the experience of a story for most general readers or players. I believe Stephen King said that horror stories intrigue a primitive part of the brain that many other types of stories can't achieve. This could be true for porn stories.
I'd say that it's as much that, as it is that porn stories largely use the pornographic elements as a hook, and then suck you in with the story. Assuming its story and characters are good, which is definitely the case here.
Other mainstream games or media cannot put too much sexual content in it because it is illegal in many countries and are harmful for non-adult audiences. But I feel this game's success is a very interesting case study in how sexual things play in how our brain is developed.
Honestly the pornographic elements could be swapped out with plain risque or implied sexual content for most of it, whilst still leaving the real meat of it intact - Story and characters.
Whilst I don't mean it to sound like a negative, the art style doesn't have the same broader appeal that other porn games have, but the that's more than made up for by the level of creativity that the genres/themes allow, which aren't really seen in western media outside of Lovecraftian type settings.