What are you thinking of, posting a sexually unexciting, TOTALLY SANE post like that?
Seriously though: I think there's much sense in what you say.
Another conflict too, surely?:
Clearly, many players, & crucially patrons of "adult" games get a serious thrill out of (you'd hope, only fantasy) inc*st - consider how many games have an unofficial, in some cases even official "patch" created for that purpose, to get fam'ly terms into the dialogs as much as possible! - so there must be a strong press of demand on developers to include it, at least as an option, if not central to their game.
I have to admit, "roll your own" (even the smoked variety) is not a turn-on for me - I'm not being virtuous here, or even thinking mainly of practical legalities: just, I don't really see the point of looking inward too much: even in fantasy, why not widen the circle to people different from yourself? - so I came to this game with a slight contortion of the mouth at the original title.
But I saw the quality in the graphics, e.g. the first two smiling, lounging, coolly smoldering girls, who didn't at first sight look much like sisters ..., & the description of the storyline (for once not a MC tragically orphaned at age 12, etc. ...), & that looked promising.
What's maintained my interest has been: (1) super artwork - the girls' *cough* well-rendered & -textured *cough* bodies most of all - (2) light-touch, (in a good sense) sophisticated, witty, sometimes sultry dialog, (3) plot winds & meanders that are (for the most part!) involving, & again (4) for me, the game's twin peaks, Heidi & Kathy - two top creations, both as sexual beings and as engaging, likeably crazy-but-not-so-mad, generous-spirited (!) characters with elements of personal depth unusual in games of sexual content. Realistic, even, though more forgiving. But in a game without the unavoidable agendas, dissatisfactions and/or frustrations, daily pressures, banal necessities or worse hardships, & human cost of real life. (In a word, "fantasy".)
So basically I'm agreeing with your last sentence, too!