The bridge of the "Andrea Doria", at a similar depth, had been flexed by the tides and current of the Gulf Stream causing it to collapse. I, however, concur with the Admiralty's depth charging the "Lusitania" s the principal reason for the collapse. Fishing nets would would have a similar effect once the wreckage was weakened, though considering the gauge of her steel, it would take a long time for that to happen.
I personally believe any and all recognizable structure of the ship should be recovered, conserved, and placed in a non-politically assigned museum. There are no human remains left under that wreckage and historically, she is critical to the 20th Century.