>>17826323US WW2 nukes were performative, not practical. They were large, and heavy, and could only be used by slow low flying bombers.
There's a reason the US could only nuke cities next to the coast that had zero defenses.
For the US to nuke the USSR they would have to cross half the european continent, over some of the largest and active concentrations of anti air defenses, and face the second largest air force in the world at the time.
By the time advancements in nuke miniaturization, or high altitude bombers, or continental missiles, the USSR is already caught up.