Umm, there are a couple of things to consider in regard with this situation.
The most active resistance or "sanctions" began in November while Strelkov had retired on August, 14. Why was the "retribution" pending for so long? Same story with Borodai. He quit on August, 7th so I still don't understand how these things are connected.
But there's something more to it and it's rather about the historical and cultural connection of the two countries. Since WW2 there has been a lot our countries have had to go through together and this mutual story cannot be just forgotten as if it had never existed. Russians have a lot or friends and relatives there in Ukraine (not to mention business connections and stuff like that) and a lot of Ukrainians are also tied with Russia in the same manner. Even when Ukraine moved away from Russia, still there were a lot of Russian stuff and Russian people inside Ukraine and those people, being Russians by nationality and having corresponding stamps in their passports, were actually belonging to Ukraine with both their body and soul. That's why I also can't understand how you can judge people so easily by only their formal status.

I do understand though that the US or whoever started all this fuss didn't have to bother with all this stuff I am talking about to launch the action; they could use any, even remotely suitable little reason, for the actual (i.e. those we may not know about) reasons to do it overpowered the reasons not to do it. IMO