It is because Khrushchev joined this area to the Soviet Ukrainian Republic. They lived there for many centuries.
But it looks that Putin is going to fix this proble, He wants to give Russian passport and citizenship to every Ukrainian who asks for it. As a result eastern Ukraine and a big part of the middle can become empty. Hey, even the true Ukrainians from the Eastern Galicia (Western is in Little Poland) might be tempted to take the bait.
Soros will have a plenty of land to build his "open society".
You prove my point... If someone doesn't do like "you" want them to do they are unpatriotic and are traitors should be thrown out ??? Is it their fault Kruchev gave thos regions to Ukraine? Or is it their fault that they speak Russian and consider themselves Ukranian??? Why is it possible to have two or more official languages in civilized countries like belgium or switzerland but in Ukraine you must know Ukranian even if you think you speaking Russian is totally fine in the region you live in.
A perfect example is the Trans-Carpathian Oblast (bordering present-day Slovakia, Poland, Hungary, and Romania as well as Ukraine proper (old provinces of Galicia and Bukovina). The people there historically called themselves Carpatho-Russians and have always rejected the "Ukrainian" ethno-political movement since it was invented in the early 1800's, and I was raised in America in that mindset too. Some of our famous poets like Stavrovskij-Popradov wrote about the great Russian nation "from the Poprad (present-day Slovakia) to the Pacific".
The ONLY reason it is in the Ukraine ("borderland") is that Stalin stole it from Czechoslovakia in 1945.
The million people there voted by about 90% to secede from the Ukraine in 1991 (as did the Russian province of the Crimea). In neither case did the Ukrainian aurhorities consider allowing such provinces. So they are stuck for at least a few more years in a "country" they don't want to be in at all.
Maybe that is because in 1991 no one asked those people if they wanted to become part of a new nation, as opposed to sticking to the one they were in.
Well, you had best take your crusade to Belgium, England, Switzerland, Germany, France, Yugoslavia, Romania, Canada and here in the USA.