General Discussion

They assume that if they're wounded, the chances of their compatriots rescuing them are minuscule, which is one major factor. Lying there maimed and bleeding out, a quick release no doubt seems preferable. That's one reason why Russian ratios of wounded to killied in action are comparatively poor. Life is cheap in the Russian army, and many of those in the suicide meatgrinder assaults are in more danger from the Russian barrier troops stationed behind them to prevent their retreating unordered than they are from the Ukrainians.

For those who've not been mortally wounded, they may have bought the Kremlin line that the Ukrainans are inhuman and a worse fate awaits them if captured, whereas with very few exceptions, in Ukrainian captivity they'll be treated far better than they are in their own lines, including being properly fed. The same can't be said for captured Ukrainian troops.

As well as being inhuman, the tactic's also stupid because a captured solder can serve as collateral in the next round of prisoner of war exchanges.