People here are talking about conscripted prisoners, but that's not what we see here. Prisoners are offered contracts with the military, and then sent to the places where Russia is attacking to be used as expendable troops in so called meat assaults.
These are conscripts - young men on their mandatory military training which lasts for a year. Instead of actual training they have been sent to guard the border because Russia didn't expect Ukraine to attack. Because of the lack of training, motivation and most importantly heavy weapons, they are more likely to surrender.
This distinction is especially important because Putin has repeatedly promised that conscripts will not be used in the war.