Germany lost a good portion of their strong young men in the war (and so the other nations). At the end, Germany was financially destitute and to intern such a large quantity each individually, would have been an time consuming, arduous, gruesome task. Putting to rest the dead quickly was a way to avert sickness and deadly diseases with the living. If say, a catastrophe happened say, in one of our large cities with such a great number to bury, most likely a mass grave would be utilized.
Doing some recent research on WW2 carrier aircraft, I came across a somber photo of CV-11 USS Intrepid burying 69 seamen at sea on November 26, 1944, the day after the devastating kamikaze attacks on the carrier operating near the Philippines.
Dept. of US Navy: USS INTREPID (CV-11) Burial at sea
U.S. Navy archive photo.
It is sad but a fact of life.