Partly translated German map about the number of jews killed under Nazi rule

Because they were run out of much of Western Europe during the Middle Ages and somewhat tolerated by the Blyat Empire, where they merely suffered pogroms and were forced into the Pale of Settlement.

Ashkenazic Jews or Ashkenazim,[a] constitute a Jewish diaspora population that emerged in the Holy Roman Empire around the end of the first millennium CE.[8] They traditionally spoke Yiddish[8] and largely migrated towards northern and eastern Europe during the late Middle Ages due to persecution.

https://en.m.wikipedia.org/wiki/Ashkenazi_Jews

The "Poland-Lithuania" that most of these migrations went to, at the time included large portions of present day Ukraine, Belarus and Russia. The regions with the highest Jewish populations prior to WW2, seem to match the borders of the polish-lithuanian commonwealth before it was partitioned by their neighbours in the 18th century. https://en.m.wikipedia.org/wiki/Partitions_of_Poland

They were in occupied, foreign territory. No German people, no rules and no law. That would be my explanation.

Know what? I posted this, it's an old repost from my Reddit which I don't use anymore. I thought: Hmm, maybe this will actually be a post about Jews (an the death of 6 million people in on of the world's most horrible crimes against humanity) which does not get projected on the current Israeli government. I erred.

My take, as a German, without looking up the historic consensus: In Germany the oppression against Jews gradually increased from 1933 until WWII started in 1939. This gave many the opportunity to emigrate. In Eastern Europe, Germany quickly invaded („Blitzkrieg“) and immediately stated rallying the Jews into ghettos and started murdering them. There was no real chance to emigrate or flee.

Edit: a typo

The pattern I see here, I think, relates to how much advanced warning the Jews of a country got

If you're a German Jew in 1933, you're under a government that openly exists to destroy you, and still have years to GTFO before it's cattle car time. Similarly, in the USSR they didn't show up until shit was pretty real, so you can maybe prepare somehow or head East (depending on how Stalin feels about it). Meanwhile, Central Europe and the Netherlands went down relatively suddenly.

Maybe you'd hope Jews in 1937 Austria or Czechoslovakia would see the writing on the wall, but in practice normalcy bias is strong, then just as now.

They were in occupied, foreign territory. No German people, no rules and no law. That would be my explanation.