The explanation is easy, it is a game made with Love, there are a ton of Easter eggs inside, it is parodic on a ton of Sci Fi shows that most sci fi fans can point out.
I played for roughly 50 hours and I like this game a lot, there are only a handful of great space operas video games and it is one of them. The sex part is an add on, while it can't be totally avoided and with the number of hours it took to develop, it is fair enough, it is not the strongest asset of the game imo, the story and fun was for me, and I like the models a lot.
Now something for YV, it bugged me that when a girl has a sexual intercourse (not foreplay/teasing with hand/mouth) with the Captain, she does not seem to really enjoy the process or comment on it thereafter, maybe you could work on it.
I hit the point with T'ris night meditation and during that scene she mentions how she feels about her physical condition during and afterwards and it was BETTER, way BETTER.
While foreplay is mostly a one sided male pleasuring, intercourse is a 2 person giving/sharing and enjoying pleasure. (maybe try to read some erotic/porn literature, it could help a bit expanding a bit on adult scenes).
Kissing is also an important foreplay part and while I understand how difficult it could be to show it with the models, you could only mention it with text but not during every intercourse/foreplay: T'ris could have done it out of the blue during the meditation night, learning it from the TV series or maybe Verity when she was rescued and resurrected, Verity giving a kiss to the Captain before leaving with her sister would have been nice as you can easily miss intercourse with Verity entirely.
Keep up the great work anyway, that was just my 2 cents. But follow YOUR ideas overall.