"After the event of universal and eternal significance had taken place—the incarnation of the Son of God—we are not surprised that God should announce and illuminate it by means of celestial beings and miraculous phenomena, although Christ was born in humble circumstances. But is is noteworthy that these heavenly visions and miracles were not given to the world as a whole, but to a small group of simple shepherds and to a few wise men from the East."
Norval Geldenhuys, The Gospel of Luke, (Grand Rapids: Eerdmans, 1983), 111.
It does seem rather strange that God would not announce his promised Savior in splendor to the entire world. But then when you look back on history, it doesn't seem so strange after all. Think back on the numerous times that God has used the weak to overcome the mighty. He seems to delight in showing his strength through humble people. Think of David and Goliath, Gideon's band of 300, Elijah at Mount Carmel, and Peter speaking to the Sanhedrin. In every case, the person used by God was an unlikely choice, but God was able to show his greatness through those who believed and obeyed him.
For you see your calling, brethren, that not many wise according to the flesh, not many mighty, not many noble, are called. But God has chosen the foolish things of the world to put to shame the wise, and God has chosen the weak things of the world to put to shame the things which are mighty; and the base things of the world and the things which are despised God has chosen, and the things which are not, to bring to nothing the things that are, that no flesh should glory in His presence.
1 Corinthians 1:27-29