I think that more-information thing may have been a tangent of my own that's not helpful when we're thinking about people and relationships. I think many readers very much want fully formed characters and unique relationships in the stories they read (though there are also readers who do just want patterns and stereotypes that they're familiar with). The question of why our society prefers the story to end at the beginning of a relationship I think must have a different answer, and may just have to do with not wanting to think about maturity (which is definitely a flaw I can see in this culture).