Mainly because it suits the propaganda purposes of western nations, but also because it is such a modern topic that is still in living memory. Give ww2 another hundred years and it wont likely be the cultural touch stone it is today.

Plus, most Western nations were actually involved in the European front of ww2 to a large degree. Ask most people about the Pacific front and the crimes committed by the Japanese empire and you won't get the same responses.

Because even Belgians don’t give a shit about Belgium.