from Putin's Russia standpoint, it is probably best to maintain fire in the conflict, without adding too much powder or lending overwhelming force to separatists. He uses Donbass conflict as "grappling hook" in the Ukraine's back, that basically prevents it from joining EU or NATO. (Current regulations deny membership to any country that has unresolved territorial claims or participates in the military conflict.) And it bleeds Ukrainian resources, destablilizes economy, etc. So, he is pretty much doing best by not winning this conflict decisively. (btw, why don't you ask yourself what EU/USA is doing right in this conflict?)