There was an additional interesting cultural correlation I heard: there are more cases in the south and south-west of Germany plus a slightly outlier in Hamburg layer. This matches apparently when there are winter holidays in schools (different in each state in Germany) and the fact the generally skiing is more popular in the south, were many people would travel to the Alps, including northern Italy, for vacation. This could possibly mean that more people from these regions brought the virus back home.
There are more explanations.
Karneval/Fasching/Fasnacht celebrations are hugely popular in the South and West and virtually inexistent in the North and East.
The east is generally poorer (so easterners travel less) and has less popular tourist destinations - except Berlin, which has been hit badly enough.
Not a tautology but yes, that is essentially what I am saying.
I just found it weird that people seem to be focusing on all sorts of factors like family structure, median income, winter holidays, Fasching/Karneval celebrations etc (which of course also play a role) while completely ignoring that higher population density facilitates the spread of a novel virus.
Can confirm for Hamburg being an exception in the north, the holidays there are often called skiing holidays because people will travel to Austria, Switzerland and Italy for skiing. I live in the greater metropolitan region and still have family in the city, and they've mentioned that everybody that they know in quarantine is so because they've returned from Austria or Italy.
