Actually, it was not. As long as Ukraine did not ally with The EU they served as a buffer, which was more convenient for Russia than controlling them outright.
Ukraine might have been internally corrupt before they moved towards the EU, but they were free.
The EU made agreements as to the nuetral status of former Soviet vassals at the time of the Soviet break up, but they since Russia hadn’t acted against previously absorbed territories the Eurocrats thought this would be the same. A colossal blunder which is kind of predictable since they don’t have a serious integral military command to advise them and they largely rely upon the US.