Because it's a meme.
How come I never think of these things myself?
You take your birthday and look up the corresponding verse in each gospel. Of course, it's a so-very-subtle way of letting you all know my birthday.
Matthew 1:19 - Her husband Joseph, being a righteous man and unwilling to expose her to public disgrace, planned to dismiss her quietly.
Mark 1:19 - As he went a little farther, he saw James son of Zebedee and his brother John, who were in their boat mending the nets.
Luke 1:19 - The angel replied, "I am Gabriel. I stand in the presence of God, and I have been sent to speak to you and to bring you this good news.
John 1:19 - This is the testimony given by John when the Jews sent priests and Levites from Jerusalem to ask him, "Who are you?"
I guess these are kind of appropriate given that Advent is almost upon us.