"Our intention is that the foreign fighters do not survive the fight to return home to north Africa, to Europe, to America, to Asia, to Africa. We are not going to allow them to do so… (emphasis added, quoted in the BBC report entitled Raqqa's Dirty Secret)
That was the "political narrative" of the Pentagon. The unspoken truth is that Uncle Sam had come to the rescue of the Islamic State. That decision was in all likelihood taken and carried on the orders of the Pentagon rather than the US State Department.
Confirmed by a BBC report entitled "Raqqa's Dirty Secret, the US-led coalition facilitated the exodus of ISIS terrorists and their family members out of their stronghold in Raqqa, Northern Syria.