The passage of time is only a part of it - the geographic separation is also a factor as well. When we went on our honeymoon six years ago (over in Germany and Austria), even though the same 80 years have passed, the lessons of that war remained in the places we went. In the form of monuments (both in terms of literal monuments as well as infrastructure, such as concentration camps, that were operational during that time), scars (buildings that retain damage from that time or had to be rebuilt), and as well as the psyche of the population to this day. All of whom are taught a more visceral history of what happened in WWII and, at least in Germany and Austria, have had to accept their role in the war and that their leadership was on the wrong side of it.
Americans, including family members of people here on this board I'm sure, went and fought during the war, no question. But outside of Pearl Harbor, the war never really reached our shores and we had a level of separation from it on the mainland that Europeans, both Western and Eastern, never did. And my takeaway is that separation explains the level of memory loss that Americans in the macro have versus Europeans.