I don't think we need a plot device to explain why nuclear weapons have returned.
>Humans discover radioactivity
>Humans develop understanding that atoms have a nucleus composed of protons and neutrons
>Humans begin to study nuclear reactions by bombarding elements with neutrons
>Humans recognize that some isotopes are unstable and can undergo nuclear fission
>Humans discover that uranium nuclei can split into smaller nuclei when struck by a neutron, releasing energy
>Humans learn that a large amount of energy is stored in the nucleus and can be released during fission
>Humans realize that fission can release additional neutrons, potentially causing a self-sustaining chain reaction
>Humans calculate the concept of critical mass, the minimum amount of fissile material needed for a chain reaction
>Humans develop methods to enrich uranium, separating U-235 from U-238
>Humans build nuclear reactors to produce plutonium-239 from uranium-238
>Humans invent techniques to chemically extract plutonium from reactor fuel
>Humans create the gun-type bomb design, which uses conventional explosives to bring two sub-critical uranium masses together
>Humans create the implosion-type bomb design, using symmetrical compression to force plutonium into a supercritical state
>Humans develop high-speed electronic detonation systems to trigger implosions with microsecond precision
>Humans successfully test the first nuclear bomb
>Humans drop atomic bombs on Hiroshima and Nagasaki
>Nuclear weapons scare people
>Nuclear Weapon Devil is born
>Chainsaw Devil eats Nuclear Weapon Devil
>Nuclear weapons stop existing
However, erasing nuclear weapons wouldn't make humans forget all of the scientific and technical breakthroughs that led to the development of nuclear weapons. They would remember all of the discoveries made in physics/chemistry/engineering.
So, logically, nuclear weapons would eventually be invented and deployed again.
And this chapter depicts that very moment.
Am I wrong?