I think part of it, besides what you already mentioned, is human beings need touch. We see with infants and children when they are not held and touched enough they have many problems. These deprived of touch children can be found rocking back and forth trying to self soothe themselves. Pets reduce blood pressure and heart rate, they bring dogs into elderly homes so the older adults can have the joy of a pet, plus it is good for their health to be able to pet the dogs, and experience touch. So, touch has a physically calming affect, plus it feels good. It’s kind of like a drug on a chemical level.
For many adults the only touch they get is sex. When a person has young children they get it also, the warmth of a baby, or a young childs hug. In fact young children can create a sitaution of too much touch, sometimes your body does not feel like your own. I think this is part of the reason new moms might not feel like having sex, their babies are on top of them all day, and it gets to be like enough already.
I think part of the draw sex has is to be touched, our need for touch, not just the sexual pleasure part. I think we are basically unaware we are satisfying that need when we have or desire sex. Kind of like craving coffee for the flavor, but not really being aware of how addicted we are to the caffeine.