* Weather: The winter months in Bethlehem are cold and often rainy. Shepherds would have been more likely to seek shelter for themselves and their flocks.
* Sheep: Sheep are susceptible to predators and the harsh weather. Shepherds would have brought their flocks into enclosed areas for safety and protection during the night.
* Tradition: The Bible doesn't explicitly state that the shepherds were sleeping in the fields at night. It simply states they were "keeping watch over their flocks by night" (Luke 2:8). This could have been done in a variety of ways, perhaps near a cave or within a pen.
Therefore, it's more accurate to say that the shepherds were likely watching over their flocks in a sheltered area near Bethlehem rather than staying in the open fields. This makes the account of the angel appearing to them even more remarkable, as it would have been an unusual occurrence for them to be out in the fields at night.