The remaining factories that were working day and night endlessly couldn't keep up with the consumption of hot weapons. Furthermore, these weapons showed extremely poor results in combat. As many of the important cities were under siege by those mutated beasts, mankind's only option was to rely on more primitive weaponry. There were times when one's body was more useful than a hot weapon.
In the dark era's most difficult period, mankind was forced to use various kinds of scrap metal to fashion together knives, swords and other weapons. Empty-handed combat became the bread and butter of every battle, but it was still very difficult to use it against the mutated beasts. As a result, the entire population of the Federation was reduced to a third, with many of the cities falling under the dominion of the enemy.