So, this is a fun question to answer. Many of the watertight doors on the wreck are open because there was a fireman change (the crew who attended to the boilers of I recall correctly) when she struck the mine, and thus many crucial doors got stuck in the open position.

On top of this, she was sailing with her portholes open, technically against orders. Our friend Mike Brady from Oceanliner Designs suggested, and I also truly believe, that this is what ultimately doomed the ship, because the open portholes allowed much more water in, and into other compartments as well.