What has developed to be enjoyable about sex, beyond neural stimulation or routine pattern is the act of feeling feeling or sensation itself. One feels and can control the feeling of another without need of the body. This is part of the agenda of the brain. Certainly the body is involved, especially as a visual object, but in passion our body feels different, lighter, more neural. Cuddling may look abnormal or strange in public because the body is not behaving as it does in any other activity. The brain is in control and using the body for its own neural stimulation. The body is minimized, almost as if the cerebra are rubbing each other.
Because you can feel feeling you can change how you feel feeling and thus you have all the interest in sadism, pain etc. which is just extreme manipulation as a manifest demonstration of mastery of feeling Dramatic horrible things can happen to you or someone in front of you and because you can control their feeling of your feeling the person has greater tolerance. The more extreme in manipulation the greater power the brain feels. When the brain controls feeling, it feels good because it has demonstrated control of the body. The brain at its primal strategem is scared of everything, even the body.