Some airlines are loooking sideways at Germany because of the impending aviation tax but FRA was a significant feeder into LH's worldwide network.
Surely there must be other reasons too though? Connectivity to Germany has been bad for years, with the exception of a short-lived Easyjet BRS-HAM route a while back, the Airbus-targetted Bristol-Bremen OLT route, and of course the Berlin route. I simply can't believe it's not possible to operate e.g. Bristol-Hamburg, Bristol-Munich, or Bristol-Dusseldorf/Cologne profitably a couple of times per week, even without feeding into a hub like Frankfurt.