To be fair (to be fair)* and clear this isn't kink shaming- it's just "porn fetishes you just don't understand", not "Oh god, things that repulse me".
These are in no particular order, alphabetical or otherwise.

(Also, not a comprehensive list)
Futa. Just who exactly is this for, in particular?
Lesbians- ladies who want a dildo with a pulse and a conversation?

Straight Women- who like the "D", but want some nice, soft booblies to play with during sex?
Gay Men- men who also like the the "D", but want some nice, soft booblies to play with during sex?
Straight Men- who are curious and it's not "gay" because of the nice, soft booblies and a woman's face?
Everyone- as other users have pointed out, "Futa" is supposed to be a woman that possesses both sexual organs, male and female, but most of the games show them having "danglies" and that would be (iirc) a hermaphrodite.
I mean, it is apparently a popular genre, but just who is the target audience?
(Not to mention, the ladies typically have MASSIVE wangs- now I'm not just upset by the fact the dev has coding skills...) Lol Oh yeah and
Rocket Wangs (M or F)
'nuff said.**
Scat/Wee/Vom

Any of the "toilet body fluids".
(and felching, if you don't know, do not look it up). (Don't do it.)
Admittedly, thanks to South Park- I did watch some "Brazilian Fart Porn"- it's not particularly a turn-on, but it is pretty fucking funny.
(Cheating)/NTR. Not only the act, but the fact that it (apparently) has more meanings that Hannukah has ways to spell it... As I've come to understand it;
Netori- you're the "cucker".
Netorare- you're the "cucked".
Netorase- you're the "cucked", but with the added bonus of a tub of popcorn while you watch yourself getting cucked.
Why can't these be simplified to "NTI", "NTO", and "NTS"? It would cut down on a lot of vitriol in the threads, if people knew which one they were trying to avoid.
Gore/Guro/Snuff/Necro/Vore
Just WHO is this for exactly?! Murderers and Serial Killers? Why would this level of extreme violence be a turn-on? There has to be some deep-seated psychological damage associated with this one. (Who the eff wants to be actually eaten?)
Internal View (Surprised no one has mentioned this one.)
Just WHO exactly is this for- Coroners? Morticians? See Above^? I can't think of single instance where I thought of the INSIDE of the person that I was with while doing the "deed(s)".
Bulging/Inflation
IF you can see visible distention of the person's body- you've most likely done some serious internal damage (THEN the "internal view" might come in handy).
Pain/Rape/BDSM (Extreme)
I can say that I want to be neither hurt/restrained in such a way that I have no control over the situation- especially, if it were to go South... Nor do I want to be the one initiating it.
Bugs/Parasites
Just why? Tentacles I can kinda understand, they're at least phallic...,but bugs? *no shudder emoji, so*
Ginormous Booblies
I mean large breasts are nice, I still prescribe to the "more than a handful is a waste", just due to the work that went into pleasing a partner with "extra padding" (My tongue has limits AND you want me to keep going?!) Lol I'm talking about these bigger than inflatable raft booblies. Y'know those HUGE ones that couldn't exist IRL (although there was that one lady with a ZZZ cup, iirc, years ago), but while they may be a turn-on for some- is anyone even considering the back problems she's going to experience as she gets older? Poor thing is gonna need a wheelbarrow just to get around normally. WHO likes their booblies THAT big?
(Also applies to behinds.) Lol
(Furry) Gay Porn
Why does it seem like a lot of the games with top-notch renders, animations, and stories are for gay men.
Also, why are a majority of these games "furry"? They're not just furry, but they're just these ripped, burly anthropomorphic characters that I call "Furlies" (Furry + Burly). If you look at most of the games for gay dudes- they're mostly "furly".
Well, that concludes my list of "porn fetishes that I just don't understand" (and why).
Honourable Mention
That "Chair Simulator" that's on this site. Lol
I have to say that playing a lot of these different types of games has "broadened my horizons", as it were, and I've found a couple things that I didn't think I would like or even know... Agalmatophilia is definitely an interesting one.
I did just recently, see "CBR" and "KBJ" in this thread. I'm not familiar with either of those...
*Surely someone will get this reference.
**R.I.P. Stan "The Man" Lee Excelsior!