Imagine the following scenario. A Ukrainian soldier asks his commander:

Why do we have to give food and shelter to the enemy while they rape and torture to death our fellow soldiers and civilians.

And the commanding officer replied:

This is a war of civilization against barbarisms and we must be the side of civilization. This might sound like empty propaganda, but has quite an effect on morale of both our defenders and the foreign sponsors of our defense.
Just think about this. We are defending our homeland against an enemy that in the beginning was almost 20 times more powerful than us. But we somehow managed to defend our ground and stabilize the situation because we are trying not to waste any advantage we might have in the battlefield. One of said advantages is making the enemy aware he can surrender before any engagement and will be treated humanely. Have you noticed how easy seems to be to make them surrender without a fight? That's because we make sure to have our PoW camps treating them better than their own commanders would. Meanwhile our own comrades fight to the very end because the enemy does awful things to their prisoners. The better alternative we give to them is what allows us to gain a lot of ground in places where they don't have the special anti-surrender brigades, which were created specially to fire against their own soldiers if they attempt to surrender.
To summarize what we intend to do is to push in their minds a simple idea: Why risk your lives for the ambitions of a dictator that treats you like crap?