In the aftermath of WW2, it surely was the post-war reconstruction (in what became West Germany at least). Later on, US cultural exports from Disney to Mc Donalds dominated. Hollywood, satellite t.v. and now the WWW have major influences (cue "Amerika" by Fee). Germany isn't a small US, there remain significant differences (for the better or worse), but travelling (later immigrating) from Germany to US, the latter seemed eerily familiar and strange at the same time.

I'd wager that kids in Germany today (or for the last 40 years or so) can relate more to Tom Sawyer and Huckleberry Finn than to Struwwelpeter, not the least because the former was made into a (quite well done) t.v. show dubbed and broadcast in Germany.