Slight correction: It’s not “the Germans” that love Hasselhoff, but a certain generation (I know, because I belong to that generation). As kellner explained in this old thread, kids in the 80s got their first impression of US series (of that time), and it was the coolest thing on terrestial TV. I, too, watched Knight Rider as a teen (and, though I can’t fathom why today, at that time I thought he was good-looking, even if the stories were dumb). So when a couple of years later his “Looking for freedom” came out, it expressed my teenage feelings of not being free quite adequately, and did for many others.
Another point is geography: while in the US it may be fairly easy to meet stars, only a couple of US stars come overseas. So if a star does the long journey, he will find more fans than at home.
But to answer the OP: I second “Sound of Music”. It’s practically unknown to the Austrian and German TV watchers, because it’s categorized as “Heimatfilm” (home country movie) - made in the 50s and early 60s in colour, showing wholesome country life, simple plots, lots of love and idyllic scenery, so people could stop dealing with real life problems and forget all the whole World War/rebuilding stuff. When, on a rainy Sunday afternoon today on public TV they are repeated, they are (stereotypically) watched only by the older generation, which loves this sentimental stuff (partly reminiscing their own youth, of course, and partly for the no-problem idyllic.)
In fact, I think the only pampleths advertising “Sound of Music” tours in Salzburg are in English, because only American tourists are interested in them. (I had to explain to my fiance what it was all about).