Why was the name of St Joseph not mentioned at Luke 2: 19?

At Luke 2:15-19 (NRSVCE) we see: >When the angels had left them and gone into heaven, the shepherds said to one another, “Let us go now to Bethlehem and see this thing that has taken place, which the Lord has made known to us.” So they went with haste and found Mary and Joseph, and the child lying in the manger. When they saw this, they made known what had been told them about this child; and all who heard it were amazed at what the shepherds told them. But **Mary** treasured all these words and pondered them in her heart. My question is: Why was St. Joseph who was also privy to the happenings around Infant Jesus, left out of mention when Luke wrote about St.Mary pondering over the incidents ? What do the Catholic teachings say about that ?