Too much panic. Hundreds were trampled. Nearly 500 killed outright when the first Russian torpedo that slammed into her port side, struck a deck that had a drained swimming pool. All that tile came loose and acted as an enormous fragmentation grenade and killed everyone on the deck but 3 people. Almost 10,000 German civilians died. 9,400 and some change, I think
Over half the dead in the Wilhelm Gustloff sinking were children. The ship was on an evacuation mission.
There are leftists in Germany today who argue that the torpedoing of the Gustloff was a legitimate act of war.