O.K. I see your point, i've entertained the idea, and "this is what I personally feel/think"..
If sex was the ice-cream, then babies wouldn't survive.. you would think that people would be having sex so often that we would be overpopulated in a matter of years; but actually, babies wouldn't survive.. People would be too busy having sex, that there would be no need to take care of babies, there would also be no formal family structure where two parters could take care of not only the babies, but eachother (with age). But don't take my word on it, that's only an idea, that's just what "I" think..
An other crazy idea of mine is.. maybe, just maybe.. emotional bonding is more rewarding than sex.. There are two basic needs in life; to replicate, and to survive.. The need to replicate will eventually be satisfied, but the urges will linger.. the need to survive however is constant; and needs constant satisfaction.. So while your desire to have sex is a lingering urge to replicate; your desire for quality companionship, emotional bonding, and connection are all parts of your ongoing need for survival.. the latter is actually more satisfying than the former.. but again, that's just how "I" feel.. don't take my word on it..