There was no room in the inn. Why? Because for 3 times a year all able-bodied males are supposed to be in Jerusalem for worship: Feast of Unleavened Bread, Feast of Weeks, Feast of Tabernacles. And the timing of the months from Zechariah's service in the temple (feast of Weeks/Pentecost), all the way to Christ's birth (the following year), brings the narrative to the 7th biblical month. The Feast of Tabernacles is in the 7th month.
Our Father lays it all out for anyone who cares to know and celebrate Christ's birthday; commanded to be remembered throughout Israel's generations. Hundreds of years long before Christ was even born of the flesh, God made sure his son's birthday was set apart as special.