Also because a single large blast wastes a lot of energy, and is easier to intercept.
You’ll do way more damage way more reliably with 20 1MT warheads than with a single 20MT bomb.
But it required reliable ballistic missiles and M(I)RV. If your delivery mechanism is bombers, then at equiv-tech you have to account for high attrition rates, and thus need large payloads to ensure even low success rates will do the necessary damage to the target.
You’ll do way more damage way more reliably with 20 1MT warheads than with a single 20MT bomb.
But it required reliable ballistic missiles and M(I)RV. If your delivery mechanism is bombers, then at equiv-tech you have to account for high attrition rates, and thus need large payloads to ensure even low success rates will do the necessary damage to the target.