The fear that steers Joseph away from Archelaus's land is that same inner guidance at work: the fragile new life must be led away from ground the cruelty still rules.
The dream gives him what waking judgment cannot see, a full picture of the danger. The holy child is still at risk from the very power Archelaus inherits from his father Herod. Warnings like this come on their own, without a person choosing them, because real growth needs the carrier of new life to reach ground where cruelty has not yet taken hold. Galilee is that safer ground, the place where the new life can slowly unfold without being crushed at once by ruthless power.