The Buryats didn't choose to be part of the Russian Empire; it was the Russian Empire that conquered them. The same rings true for the rest of Siberia and Central Asia, which the Qing Empire never had dominion over.There’s a certain sense of cold hearted schadenfreude I feel re the buryats as I do towards the mongols and other former denizens of previous Chinese empires; these guys chose to become a part of the Russian empire, well suck it up and enjoy being cannon fodder as the non white draftees for mother Russia today. Your cousins in Inner Mongolia are getting fat and rich off Chinese growth.
As for Mongolia and Tanu Tuva, the Soviets defeated the Beiyang army in the 1920s, which resulted in China losing those territories. Had China not been embroiled in constant turmoil throughout the 1910s, Mongolia and Tanu Tuva would still be part of China. Sinophobia in Mongolia today is the result of leftover Soviet propaganda after the Sino-Soviet split, which America has no doubt taken advantage of to incite even more Sinophobia.
All these migraines emanated from China's weakness throughout the previous century. Be thankful the CPC was able to wrestle Tibet, Xinjiang, Inner Mongolia, Dongbei, Hong Kong, and Macau back.