Well yes, and in this case we're talking files that contain an exploit for a version of Acrobat from 2006 or so and an infection vector that only works on Windo

Well yes, and in this case we're talking files that contain an exploit for a version of Acrobat from 2006 or so and an infection vector that only works on Windows XP, and connects to a botnet that is either long dead or now an NSA/CIA asset. But Windows Defender quite rightly still quarantines the file.