I didnt get any if the ones below 50% weird how some I have never even heard off. (Saarbrucken and mainz sound familiar and magdeburg rings a bell, but the others... new to me !)
Potsdam: residence of Prussian kings such as Frederick the Great (Voltaire was a regular guest at Sanssouci castle). Site of the 1945 Potsdam Conference where "The Big Three" Truman, Stalin and Churchill (famous photo) discussed the world's postwar order.
I don't get why Frankfurt isn't the capital of Hesse? Why choose Wiesbaden when Frankfurt is an option, especially since Frankfurt is more central and Wiesbaden even borders Rhineland-Palatine? Normally you would take the largest aproximately central city with a proper city center, ergo Frankfurt...
It turns out that, after World War II, when Hesse was founded, Wiesbaden was selected as a provisional capital. Subsequently, as the division of Germany made it clear that Berlin could not be the capital of the Federal Republic, what with being surrounded by another state, Frankfurt did not seek to become the capital of Hesse, because they were absolutely sure they would become the federal capital. They were the biggest and most historically significant competing city, they had an airport, and they even started building a Parliament. But then, Bonn won, for only two reasons: it was small and insignificant, so unlikely to outshine Berlin in the event of reunification, and it was close to home for Adenauer. So, Frankfurt got stuck with nothing. Serves them right.