Why was it posthumous?
he continued to deliver the fire of his skillfully improvised weapon at a tremendous rate of speed which rapidly exhausted his ammunition. Undaunted, he removed his helmet and shoes to expedite his movements and ran back to the beach for additional ammunition, making a total of 8 trips under intense fire and carrying or assisting a wounded man back each time.
Later in the day, although his weapon was twice shot from his hands, he personally covered the withdrawal of his platoon to the company position
He ran himself out of ammo nine times, had his gun shot out of his hands twice, and, being a Marine, he did not quit nor would he run out on his fellow Marines. And, it being Iwo Jima:
Stein was wounded during the fight for Suribachi and evacuated to a hospital ship. Meanwhile, his regiment advanced up the west side of the island until reaching the strongly defended Hill 362A, where they took heavy casualties. When Stein heard of this, he left the hospital ship and returned to his unit. On March 1, he was killed by a sniper while leading a 19-man patrol to reconnoiter a machine gun emplacement which had Company A pinned down. Thanks, Marine. Semper Fi.