Capturing is very high risk, and will cost you troops. Unless they actually surrender, capturing is not even considered. Also, taking prisoners is a huge burden when your country is being overrun by a superior force. Badly needed troops are sucked away to deal with transporting, housing, guarding, feeding and providing medical care for them.
Ukrainians are fighting and dying for their own soil, no different than if you were fighting foreign invaders in Georgia. A policy of "don't kill the invaders if you don't have to" isn't really reasonable. The deaths of Russian soldiers are 100% on Putin.
https://freerepublic.com/focus/f-news/4047546/posts
And of course this is not gonna escalate the war at all right?