After German reunification TWA, Air Canada and Singapore Airlines started flying to Berlin. Lufthansa even had flights from Berlin to Tokyo and Washington. People assumed, like the OP, that the capital of reunified Germany would generate lots of traffic, but all these flights were gradually dropped, and after 2001 they all disappeared. For a while there were not even direct or non-stop flights from Berlin to New York, but then Continental and Delta started theirs up.