I think DNR forces begged Putin to help them during Mariupol seize in 2014. Putin didn't do anything and went for Minsk Agreement. I think Putin didn't want any escalation after the Crimea take over because the Western media depicted it as an act of war. I understand there is little he could have done in 2014 but Donbass people suffered the most in this 9 years of war and still suffering.