>>People asked, why let them go?

It's pretty simple: The UAF cares about civilian casualties and infrastructure - in contrast to the RF. Getting the RF to leave without any 'last stands' means fewer Ukrainian civilians die. I'm sure they hunger for retribution over the many war crimes committed, but the focus has to be on countrymen and women still alive and buildings still standing.

Also, no pitched battles means more military forces fit to push the RF out of the rest of the country.