I've just seen the Kaer Morhen love scene and asked myself the same question. It was probably a clumsy attempt to replicate the atmosphere of the terrific TW2 bathhouse scene, but with TW3's turn towards prudishness.
The toned down erotic content of the game is an especially unpleasant surprise in light of the exaggerated gore during swordplays, including the gratuitous slow-mo decapitations and dismembering. With this, CDPR has safely subscribed to the norms of the predominant majority of popular culture, in which a proper sex scene is deemed just damn too risky. Nothing new under the sun or even surprising, just disappointing. I don't even mind the over-the-top orgasm of violence, but it strikes me quite hypocritical when the game's sexual content is hiding under the cover of PG-13.
Is this the biggest problem of the game? Not by a long stretch, IMHO. But as it has been pointed out before, regression rarely works in favor of quality.
The hypocrisy is indeed disappointing though not surprising. Not only is gory combat acceptable, the prevalence of scenes of intensely vile brutality, depravity and grotesqueness are also allowed e.g. figures impaled on stakes through their orifices, the mutilated prostitutes in Junior's pad, etc. And yet, a few extra seconds of explicit intimacy is off limits.