Because it is not true. With the exception of Crimea, those regions are majority Ukrainian, not Russian. Those fake referenda that Russia conducted are not worth the paper they were written on. There is a reason that Russian blocked the referendum that, in accordance with the Minsk Agreements, Ukraine was preparing to conduct in Donbas.
Who gives a hoot? The vast majority voted for Yanukovych and refused to be part of a government formed illegally.
They sought their independence and, then, voted to join the Russian Federation.
Nothing will change that.
Whether you like it or don't like it, start learning to live with that fact.