Why surviving forces would rebuild instead of launch a broken-back attack

After a nuclear war, would the surviving conventional forces launch a final broken-back attack?

Probably not; those forces would be needed for population control and reconstruction, while another attack could waste them against destruction, defences, and radiation.

The proposed attack consumes precisely the conventional units needed after a nuclear exchange. Surviving governments would need them to maintain order, assist civilians, and begin reconstruction. Sending them against an enemy that might already be destroyed could expose them to prepared defences and residual radiation. Preserving those forces for domestic recovery is the preferred practical response in this hypothetical.