You obviously missed the point
It has nothing to do with modern, things DID change after the war. Almost every gadol forbid leaving Europe for either the US or Palestine that is not an opinion. They all said one should stay in Europe. That is a fact.
After the war it was impossible to stay in Europe, that is also a fact. Not being modern , It is a fact.
Of the few Gedolim who survived the war including the Satmar Rav who clearly before the war forbid people to leave Europe, even he left forst to Palestine and then settled in the US, which he expressly forbid before.
Of all the Rabbanim who survived the war, how many stayed in Europe after?
Things did change, whether you want to admit it or not. The future of yiddishkeite no longer was in Europe, but in Palestine and the US.
And finally let us not forget communism, most of the jews lived before the war in countries that would become communist and religion would become forbidden there. The jewish community did not get back the Building for Yeshiva Chamei Lublin which was finished in 1930 and closed in 1939 until I think 2004. And it is STILL not totally a yeshiva, its partially a hotel