No Room for Random
"But after Joseph had considered this, an angel of the Lord appeared to him in a dream and said, 'Joseph son of David, do not be afraid to take Mary home as your wife, because what is conceived in her is from the Holy Spirit." Matthew 1:20
God did not choose Mary and Joseph at random. The fact that both Matthew and Luke take the time to identify Joseph as a "son of David" was enormously significant. If Jesus was going to be believed to be the Messiah to the Hebrew people, then he would have had to have been a descendant of King David.
"The LORD declares to you [David] that the LORD himself will establish a house for you: When your days are over and you rest with your fathers, I will raise up your offspring to succeed you, who will come from your own body, and I will establish his kingdom. He is the one who will build a house for my Name, and I will establish the throne of his kingdom forever." 2 Samuel 7:11b-13