Well, you can moan and shout about it all you want, but at the end of the day the ones that make decisions about the game are the Devs and they are not even in this forum (as fas as I am aware).
Also, adding something like Sex to a game is not as easy as you might think. I mean, yes, you can do it in an afternoon but then it will look like shit, be broken as fuck and the same people that asked for it, will immediately turn around and bitch about it being bad.
If you want to do it properly it will take Weeks, if not months to lay the groundwork in the game engine, rework all the character models, script and animate the "Act" and troubleshooting possibel game breaking bugs. And after all that work you still need Steam to approve everything, because the game is being sold on their platform and they might not be happy with the thing you added, making all the work worth nothing. Yes, I know that there are other NSFW-Games on that platform, but Steam swinging the big Ban hammer is always a possibility and a chance some Studios do not want to take, having just spend a lot of time and money on something.
So, how about you people stop crying about a game, that has already more adult content then it was supposed to, not having enough pixels moving around in a lewd manner. The game has modding support so if you really cant live without it, then go ahead, make a mod for the game that adds Sex scenes. After all, like you said yourself," It shouldn't be that hard to add sex in it", right?
We all should be happy that the Devs are able to full fill their dreams for the game, after all, creating a game should be about making something that you, the Developers, are proud of, not something that some horny guy on the Internet, that just noticed that the game had an update on a Pirate Site, wants.
So yeah, please respect the decisions the Developers made for the Game, after all, without them this game would not be a thing.