The really big weapons come from an era when delivery systems were really inaccurate and so you'd drop an absurdly big explosion somewhere near your target. Onc

The really big weapons come from an era when delivery systems were really inaccurate and so you'd drop an absurdly big explosion somewhere near your target. Once you can hit your target reliably you go with a smaller explosion that's still sufficient to destroy it when dropped on top of it and you stick multiple independent warheads on the same missile.