The same logistical situation is why so many POWs captured by the Allies in Europe and North Africa were brought back to the United States

Well, that and the fact that it completely takes them out of the theater of war. They’re not going to be rescued and released from a camp in the middle of Montana.

And even if a few do escape, they’re a few days walk from anywhere, and will stick out like a sore thumb if they did encounter a local.