These conditions would exist in a battle that involved the movement of settlements along with the military. That is the hint we have of the movement of Coriantumr in verse 15. With the tactics of Shiz destroying the settled populations, there was no safety for stable populations. Therefore cities would be abandoned prior to the arrival of Shiz.
The lack of local populations remaining in the area accounts for the inability of the bodies to be properly taken care of. The battle continues, and the populations are consistently under pressure. In other circumstances, local populations would remain to deal with the aftermath of the battle. Here they are not present, and the bodies of the dead simply lie on the ground.