Yeah why? Apart from the fact that actually the Soviet Union bred People's Republic of China. The help provided during WWII (military supplies, volunteer war pilots and the overall successful liberation of China from the Japanese troops by the Red Army) and after (establishment of basic branches...
Lost knowledge regained... It's like humankind's head emerging from the water of the Dark Ages following the Great War, its lungs catching the fresh air of short enlightenment. Though often they still catch nothing but the smell of smouldering rubbles.
Scarcity or lack of information sources...