I don't think that the reasons for marrying are as far removed from primate (or mammal, or animal in general) mate selection as people think they are.
Or more likely, people don't realize at all the degree to which their behaviors and decisions are instinctual, and are confusing the rationalizations that are layered on top for the actual explanation.
For that matter, if the couple procreates, they have validated whatever biological forces brought them together, regardless of their happiness or longevity.
Neither is anything at all like the decades-long commitment of a good marriage. While it may seem like sex is the main feature (and it is important), as someone who maintained a relationship for twenty years (she passed away five years ago) I can assure you that it's far from the only factor involved.
I am led to believe that human marriage is much more than just animal mating. In a liberal society, such as the western countries, where mating before marriage is common, I don't think there is any confusion between the two.
Your comment might be more applicable to eastern societies where mating before marriage is taboo. One only get to mate with the one they "chose" to marry.
Or more likely, people don't realize at all the degree to which their behaviors and decisions are instinctual, and are confusing the rationalizations that are layered on top for the actual explanation.
Why do two dogs choose to mate?