Adam Clarke on Luke 1:26

A city of Galilee - As Joseph and Mary were both of the family of David, the patrimonial estate of which lay in Bethlehem, it seems as if the family residence should have been in that city, and not in Nazareth; for we find that, even after the return from the captivity, the several families went to reside in those cities to which they originally belonged. See Neh 11:3. But it is probable that the holy family removed to Galilee for fear of exciting the jealousy of Herod, who had usurped that throne to which they had an indisputable right. See on Luk 2:39 (note). Thus, by keeping out of the way, they avoided the effects of his jealousy.