Zdad
The Holocaust is very clearly an exception. Its not something that ever happened before and nobody imagined that someone would take over entire continents and kill all the Jews. This never happened before in history. In the past we got bounced from country to country within a close radius give or take. It never was an issue of switching continents and travelling so far away.
My next point is slightly controversial but I will say it anyways because its the emes. At least the concept is. There were many people advised not to go to the US due to the spiritual nisyonos. It is better to die al kiddush Hashem as a frum kosher yerei shomayim than live a long life as a Jew who threw it all away. I have relatives who came before the war. They are all totally not frum totally. And they came from strictly chassidish families. No Yiddishkiet left by them they all threw it all away. So maybe min Hashomayim Hashem knew that many of these people were not strong enough and therefore put it into the Rabbonims minds to advise them to stay.
I have an additional possible scenario and that is that at the time the shayla was asked maybe it was possible that there was no gezeirah yet on Hungary and for whatever reason Hashem decided to add Hungary into the mix at a later point.
However throughout our history it has always been the practice of those who want to do dvar Hashem to seek counsel by Tzaddikim. Baruch Hashem this still goes on today. I’m not saying every Rabbi is qualified in this respect but certainly the Gedolei Hador the ziknei hador are qualified in being asked advice in all matters. If they really don’t know they will say I don’t know. That’s also Gadlus.