Why would a civil war soldier eat hard tack?

At the time of the Civil War there were only a limited range of food preservation techniques, which were not as sophisticated as the ones we have today. Military food has to be easily portable, easily prepared, and relatively imperishable; soldiers do not carry refrigerators or ovens with them, and war is often about marching great distances in pursuit of, or in retreat from the enemy forces. Hard tack fit those requirements, and it was often the best that could be managed at that period in history. Today, soldiers fighting in Afghanistan have much better food options.