Finn has been a popular name in the north of Germany (especially in Schleswig-Holstein in the very north) for some years now, but I can't think of any special reason for that.
Finns in northern Germany are about 0-20 years old at the moment. The popularity of the name has spread to the middle of the country a bit later, so the Finns from there are usually younger. I haven't heard about
Finn being used in the very south of Germany or in Austria and Switzerland, yet.
Yes, there's no real statistics of
German first names considering ALL births - unfortunately. So this top 200 you found is probably the closest you can get.
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Satu
http://www.nordicnames.de/Aussprache.html