For me it was DC and the relative ease of getting to *G. Combine this with the fact that MME is my local airport I used to use BD through LHR and connect to other *A carriers or even with BD when they flew to somewhere I wanted to go. For TATL I drove to MAN and enjoyed the service in C immensely.
Now I drive to NCL or still MAN (MME and LBA are both useless IMHO)
In the end they withdrew all the decent routes and now I have SEN with LH through LH's status match I dont see how I will use BD. 90% of my *A flights this year have been LH or SN so I hope M&M means something there.
Sadly BD cancelled all the routes I spent money on with them. I am sure i am not the only one. A great airline. As someone once said there are no such things as bad companies just bad management!
I know the OP wanted reasons to return and I would do if they sorted out the mess they have made of what was once a great airline. I really have tried to use them because of the past wonderful experiences but I just cant find schedules, connections or an airport nearby to fly from with BD!