That's because at the time the Russians wanted to pretend they didn't do anything. There were no little green men. Since then Putin has acknowledged that it was in fact regular Russian troops that were on the ground.

Or just listen to what Igor Girkin is saying. He was the guy who organized the Russian special forces that took over the regional administrations in the Donetsks and Luhanks regions. Girkin then served as a "minister" in the DNR "government". He had nothing to do with the region, but was from Russia proper. Just like most of the "officials" who served in the DNR and LNR "governments". However, to be able to listen to his podcasts you would actually have to learn Russian.