Les nôtres

I really want to know what film makers had in mind making this film. Almost two hours of useless story that just in few minutes it's main plot is revealed. It's about a teenage girl that is pregnant, throughout the film all adults ask about the identity of the father and she refuses to answer, so everybody goes to their "normal " lives. Film makers fail to show us who this girl is and why she is acting like this, the mother just accepts the fact that her thirteen year old is pregnant, my guess is that the director really enjoyed disappointing the viewer for revelation of the truth.