Are they really unaware or do they actively deny the cultural connections? Prussia was a thing not that long ago - it is still used as a slang term for Germans in parts of the Netherlands ("de Pruisen" of "die Preußen"). Anyone who had a bit of history or who has looked at an older map sees that Prussia was divided between what is now Germany and Poland. Of course both countries went through a lot of upheaval between then and now but there's still plenty of people alive who will remember living in Prussia.