They have to start that way because they are stories about "magical and imaginary beings and lands" that obviously, never really happened.
In stark contrast, we have Luke 2 and the events described in it.
They really happened.
And in Luke 2:1-4, God, through Luke, drops a pretty big historical name - Caesar Augustus.
"In those days a decree went out from Caesar Augustus that all the world should be registered. This was the first registration when Quirinius was governor of Syria. And all went to be registered, each to his own town. And Joseph also went up from Galilee, from the town of Nazareth, to Judea, to the city of David, which is called Bethlehem, because he was of the house and lineage of David..."
With that name, we've got a person, time and place in the timeline of history whose existence and power are not disputed. He really lived.
Caesar really ordered a census and Joseph and Mary really went to Bethlehem to register. No "once upon a time" here. These aren't magical and imaginary beings and lands. This was God and Nazareth and Bethlehem and Caesar and Mary and Joseph.
God showed off in a spectacular way during this real historical time with these real historical people. He caused movement of people and events on a world wide scale!
That is our very big God.
Our very real God moved - and is moving still - in our/your very real world.