Mary was not just some random teenager selected by God. This is why God chose Mary.
Mary's descent comes through David's son Nathan, Luke 3:31. To fulfill God's promise to establish David's throne forever, God honored Nathan by making him the ancestor of the promised King (Messiah) who would sit on David's throne throughout eternity, Luke 1:31-33. Mary having no brothers to inherit the throne the inheritance would come to her first son being Jesus.
This is why God found favor only in Mary as still being a virgin before she married. Joseph descent from David was broken in being heir to the throne of David as one of his ancestors named Jeconiah (Coniah) was so evil God cursed him and his descendants from ever sitting on the throne of David, Matthew 1:1-17; Jeremiah 22:24-30; 1 Chronicles 3:17. This doesn't mean that Joseph was evil, but means none of his children could ever sit on the throne of David.
The genealogies in both Matthew and Luke, although they differ, are about Jesus'
male ancestors; they have nothing to do with Mary. If there is a place in Scripture where it says that Mary's descent comes through David please let us know.
You wrote, " Jeconiah (Coniah) was so evil God cursed him and his descendants from ever sitting on the throne of David," But Jeremiah 28:4 says, "I will also bring back to this place Jehoiakim’s son King
Jeconiah of Judah and all the exiles who were taken to Babylon.’ Indeed, the Lord affirms, ‘I will break the yoke of servitude to the king of Babylon.’”
The genealogy in Matthew says, "This is the record of the genealogy of Jesus Christ, the son of David, the son of Abraham.
Abraham was the father of Isaac, Isaac the father of Jacob, Jacob the father of Judah and his brothers, Judah the father of Perez and Zerah (by Tamar), Perez the father of Hezron, Hezron the father of Ram, Ram the father of Amminadab, Amminadab the father of Nahshon, Nahshon the father of Salmon, Salmon the father of Boaz (by Rahab), Boaz the father of Obed (by Ruth), Obed the father of Jesse, and Jesse the father of David the king.
David was the father of Solomon (by the wife of Uriah), Solomon the father of Rehoboam, Rehoboam the father of Abijah, Abijah the father of Asa, Asa the father of Jehoshaphat, Jehoshaphat the father of Joram, Joram the father of Uzziah, Uzziah the father of Jotham, Jotham the father of Ahaz, Ahaz the father of Hezekiah, Hezekiah the father of Manasseh, Manasseh the father of Amon, Amon the father of Josiah, and Josiah the father of
Jeconiah and his brothers, at the time of the deportation to Babylon.
After the deportation to Babylon,
Jeconiah became the father of Shealtiel, Shealtiel the father of Zerubbabel, Zerubbabel the father of Abiud, Abiud the father of Eliakim, Eliakim the father of Azor, Azor the father of Zadok, Zadok the father of Achim, Achim the father of Eliud, Eliud the father of Eleazar, Eleazar the father of Matthan, Matthan the father of Jacob, and Jacob the father of Joseph, the husband of Mary, by whom Jesus was born, who is called Christ."
Notice that Jeconiah is mentioned in Matthew's genealogy of
Jesus. Biblical descent is reckoned through the
males, not the females. Mary is mentioned only parenthetically as Joseph's wife.