The reason is that at least theoritically, the communist philosophy is peacefull. Not only because Russia suffered too much because of the War but because theoritically the War is an Imperialistic tool. So when you speak for the 1st world war, then for the 2nd world war, obviously you are waiting for another war the 3rd one. In order to avoid this, Soviets were speaking for the Great Patriot War. Many writers from the western world also they do not use the term 2nd world war but they use the term: 'the Last War' wishing to point that this terror world faced between 1939-1945 was the last one.