Sex and death/boobs and gore are how trashy horror movies thrive.
I don't really know many horror games, but i do know that Resident Evil ones with a female character have nude mods, The Forest's cannibals were all naked at some point (i saw boobs and got interested in the game, so... :shrug: eh) and there was this one guy on reddit (i think) who exploited a dismembered NPC resurrection bug + prostitution mod in Fallout 3 or NV just because.
The fascination with death and eroticism has a very long history. They even made a documentary about it (or a couple), which i don't really remember, but i think they talked about the meaning behind sexualizing vampires, witches, the Inquisition, necromancy, self-flagellation and other stuff (or i'm just mixing up my documentaries). So, it's not that weird a fetish in actuality as it is quite widespread, regardless of culture or belief, but simply not well liked.
Remember Firefly? There was a group of space cannibals that raped, killed and ate their victims - not necessarily in that order. Or Warhammer and its Chaos.
The fetish exists and is used quite a lot in media, but i think it needs to be used in a certain way in order to avoid the wrong type of attention. I don't know what that way is, but while few people will admit it, sex and death used properly can and will attract a crowd - even if just to look from afar, in the shadows, covered up by 50 shades of gray clothing.
I remember a random Firefly topic and they talked about the cancelled Season 2 Inara death scene. They said it was planned for her to be captured by the space cannibals. The crew would then track down the ship and board it to mount a rescue. Instead they would find everyone already dead, with Inara having used a rape-revenge kind of poison that kills a rapist painfully. So it would have suggested that she was raped to death by the entire ship crew, but still got the last laugh in the end.
Everyone (the loudest voice) said it sounded like a cool death scene, a "fuck you" from beyond the grave. While it falls in the "sex and death" category, it has what most porn games most definitely lack: a proper story, a likeable multi-faceted character, a unique feat of legendary acomplishment.
With that stuff being said, i simply can't see porn games that focus on this particular fetish both multiply and succeed in drawing enough popularity to make it a standard genre. And yet, the "Similar threads" box below this shows me recommendation requests for guro and ryona...