Horror-WWII movies start out with two major plot problems, in my opinion. Well, three if you count Mickey Rourke.
The first problem is, Why didn’t they just bomb the Bad Place until it was a hole in the ground? And the second is, No, really, why didn’t they just bomb the Bad Place until it was a hole in the ground? The Allies spent the last year of the war making rubble bounce across Europe: all somebody would have to do to get Site X added to the list would be convince one general officer there’s something bad going on there. Witch-magic is all very well, but if it could shrug off incendiary bombing raids then the history of modern Central Europe would look very different.
You can get around that: OVERLORD, for example, sets up its zombie premise by staging the action during D-Day and tying up the loose ends. But if there’s a bunch of witches somewhere ‘behind enemy lines’ that’s eating soldiers, the soldiers are going to notice. And then out come the flamethrowers. Hell, witches might not even be the worst thing they’ve seen in that war…