Why did explosives become a greater threat to safes after World War II?

After World War II, explosives became a greater threat to safes primarily because the knowledge and practical use of explosives had been widely disseminated during the conflict.1

As safe and strong-room locks became increasingly sophisticated and effectively unpickable, criminals shifted their tactics away from manipulating lock mechanisms. Instead, they began using explosives to blow the locks off entirely. In response to this threat, safe manufacturers developed defensive measures, such as incorporating secondary bolt systems that are automatically triggered by the force of an explosion, preventing the safe from being opened even if the primary lock mechanism is destroyed.1