Perhaps it failed after the aircraft attempted to become a submarine regardless of the crew's intentions?
Seriously, the failure mode for the tail is not possible to create in the air unless God reached down and swatted it on the nose. It can fail in that mode upon hitting the water with some forward motion and a pretty stiff downward motion. By then the plane is breaking up very rapidly and no more messages of any kind are leaving the debris field.
{o.o}