The development of nuclear weapons in the Cold War era had much different laws and implications than it does now. The want to obtain nuclear weapons and be able to tell the world you're a nuclear state isn't only for the ability to drop a nuke on another country. Many can argue today the theory of deterrence is much more important when analyzing nuclear power rather than setting off nukes themselves. Deterrence theory is the idea that the threat of ones nuclear strength is enough to keep another country from initiating any nuclear force. The main reason all of these countries are so adamant on obtaining nuclear arsenal is to be able to hold that position on the world stage. A possession of the worlds deadliest weapon guarantees a movement up the list of countries to take notice of.
The creation of mutually assured destruction (MAD) was enforced by all participating nuclear countries. This recognizes that if one country was to set off a nuclear bomb, the receiving country can retaliate with just as much damage, in the end destroying the world over and over again. This idea proves that no enemy is willing to risk the loss of their cities over any political strain or ideological differences.
Another huge implication of why nobody wants to detonate a nuclear weapon is the environmental and health impact it leaves on the world short-term and long-term. A nuclear explosion can result in cooling of the atmosphere, shorter growing seasons, and death of all areas of the earth affected by radiation or fallout. Ionizing radiation can instantly impact the area of nuclear deployment. Delayed effects include radioactive fallout inflicting damage for many years to come. Anyone in contact with the radiation or fallout is susceptible to long term health consequences such as cancer and genetic damage.
The lack of desire to actually detonate any nuclear weapons has even developed into "nuclear-free zones" across certain parts of the world. The UN established this practice to keep certain areas a safe space from the threat of the deadly weapon. Many countries across the world's number one desire is peace across the world and nuclear weapons go the opposite of what these countries want spread in the world.