As for FRA's success - it really is about location, location, location. Millions and millions of people live within a two hour travel time of FRA, it is very centrally located in Germany and in Europe and the major industrial zones around Stuttgart, Mannheim and in the Ruhr region are all close by. The banking industry in Frankfurt generates a lot of business travel. And, as others have said, the high density of US military bases in the surrounding area back in the day helped a lot.