In the case of custom character genitals, I can't imagine the payoff in customer enjoyment being worth the effort of implementing it in a satisfactory way.
You really can't imagine people enjoying genitalia?
I certainly applaud your prioritization of what is fun in video game design; but I feel like you are woefully underestimating how much fun people can have with their genitalia.
I feel like you're intentionally misunderstanding me, but obviously that's not what I said.
I said that the increase in customer enjoyment, and subsequent increase in sales, wouldn't be worth the effort put into the feature. In fact it would probably be detrimental.
Imagine Skyrim, but now you can give your Nord a massive floppy dong. That, in itself, isn't hard to do. Many mods do this, adding jiggly boobs and dongs. Does this increase enjoyment? For some people, certainly. It doesn't, however, add much gameplay. Said enormou-dong would first have to have some gameplay function, so now the level of effort is higher. If you want people to care about this feature, now you have to figure out how to make massive schlongs a gameplay feature. You also have to do this in a way that you somehow don't come out of it with a rating that severely restricts your customer base. Some people just won't buy such a game, some cannot due to age restrictions, some because their parents/SO won't let them. It's not really worth it if you are trying to make a widely applicable commercial product.
Niche sex games can get away with that sort of thing, their restrictive rating is actually a marketing bonus rather than a penalty. They don't expect to make the millions and millions of sales Skyrim has.
Let's say instead that they just go the route of "Okay here, you can customize your cyberdong 9000" but otherwise the game doesn't change. In this scenario you likely never see the cyberdong outside of 5-6 optional romance culmination cutscenes. Is it worth the development effort? You can now have blinking lights on your ta-tas and a dong that sings a melody when your pants drop, but does this actually do anything to the gameplay?