Life has seemingly a different value in war and peace. It's highly valued in peacetime, yet in wartime lives are spent for seemingly little gain and instead of material expenses.
Here's a scenario: It's a commander's choice (the expected outcome being the same) whether to accept the loss of few infantry at a high ammunition expense or to accept the loss of much infantry at a small ammunition expense.
The normal peace-time answer would be to minimise casualties because life is being valued highly in comparison to lifeless (aqnd already paid for) ammunition.
So why is this peacetime (and cabinet war) answer not representative for great wars as well?
The economic science has an answer: Market prices depend on choices, not on some constant value. The market price is in this scenario the relative price (severity of loss) of life and material.
Ammunition is in short supply in great wars. The preferable choice is therefore to economize its use; to prevent the worst and achive the most with given material resources (high payoff uses).
The purposes with smaller payoff have an insufficient priority and don't get enough material for a material-heavy answer to their problem. Life is still more valuable than lifeless matter, but blood is the only available currency in those cases.
The scarcity of material explains why even in situations where life and material are (ner-)perfect substitutes, life needs to be expended. The material scarcity drives up the price of material (which is a lesser way of expressing the problem because at that point there's no real analogy to a market any more).
In other words: Opportunity costs are manipulating the price of material. The expense of material in one place for saving few lives would be paid for by not being able to expend the material to save many lives elsewhere. This opportunity cost is understood and drives the relative price of material up in comparison to life.
This view shows how life actually stays highly valuable, just as in peacetime; the problem is that you need to expend it because you lack the means to save it.
In the end, much more wartime bills are paid for with blood than peacetime reasoning would suggest.
Why is material typically in short supply during wars?
Material is expensive and great wars are rarely likely enough to prepare for them in excess of the societies' ability to sustain the effort in the long run.
The potential consumption of material is much greater than the potential production, especially for ammunitions. It's a bottomless hole.
Another reason is that the expectation value of lives saved in a possible wartime does simply not cut it against the "expectation value of lives saved" by other measures than piling up military hardware (such as health care, environmental protection, safety regulations...).
On top of that the individuals of the society want to enjoy the fruits of their work through consumption.
There's at least one economic science approach that could explain why the value of life relative to the value of lifeless objects seems to shift between war and peace.