"1940s tech" is like saying saying any use of electricity is 19th century tech so why can't nigger societies generate it on their own?

The truth is, this 1940s tech has gone through numerous iterations since the original trinity test, on the design and materials required to produce nukes of varying physical sizes and yields. Nukes produced the first instance of global MAD, even though chemical and biological weapons were used well before their development.

A terrorist org isn't going to organically produce a nuke anytime soon, just as MANPADS are ridiculously rare compared to the run of the mil RPG, enough both accomplish the same end goal - a propelled explosive aimed at target.

You could apply your argument to something like plasma projectile weapons - those are 90's tech that was immediately classified after it's first public indication of viability (see Project MARAUDER).

Now I would question the operational status of every nuclear nation's arsenal.