The willful ignorance never ceases to astound. The Red Cross and other organizations spent years after the war helping surviving family members locate one another. That's how much of my family ended up in the US in the 40s and 50s - the survivors still in Eastern Europe were put in touch with the remnants that had made it elsewhere. If there were anybody else still in Poland or Russia, they must have tried very hard not to be found. Highly unlikely, given that family would be the only support system anyone had left at that point.
Somehow, Dogzilla and his ilk would have us believe, all those untold millions of displaced Jews simply didn't care that their relatives and friends were looking for them, or that anyone would think something bad had happened if they just did nothing for the next few decades and pretended everything was hunky-dory.
For crying out loud, Israel Radio still has a daily call-in show to help try reuniting family and friends from the WWII era. Every last shred of information on people is submitted and broadcast in the hope that somebody might remember something, maybe make a connection. Any successful reunion - there have been a few over the last thirty (IIRC) years that the program has run - is trumpeted precisely because of its rarity.
But that couldn't be, could it Dogzilla? Much more reasonable to believe that all those places, "anywhere that has a large Jewish population," in your words, are just huddled masses of subhumanity, not communities with actual, caring people in them. You know, because mishpocha isn't important to yidden or anything.