Mary was hardly in the background in the first two Chapters of Luke. As for our veneration of Mary, it is of an entirely different sort that the Apostles would have paid to the person of the mother of Jesus. She does not seem to have traveled with him in Galilee. They could hardly have know about the circumstances of his birth from him. Until after the Resurrection, they would have thought such a story to be as preposterous as moderns today do. We dont know how Luke and Matthew came to include the stories in their Gospels. Marcion, who made Luke his only Gospel, left off the first two chapters because the doctrine of the incarnation did not fit his theology.
You raise a very good point here that I have often pondered.
Scripture never records Jesus telling the Apostles about His birth or life before His public ministry so from whom did the Apostles learn about it?