Perhaps a significant proportion of passengers to FRA via LH were using it as a connection? Did FlyBe codeshare to provide connections? (Excuse me if I didn't look back enough on the thread to say this was so)
It's easy to assume that connections via FRA will be to exotic destinations, but quite often European destinations can be reached via there that have no direct flight from MAN (I once did NAP though apparently it's now easier via MUC) or it's just cheaper/easier (done BCN twice).