It’s odd, because I have known families who have adopted Chinese children (from orphanages in China) and haven’t had this problem. Granted, not every Russian child has this disorder, but it does seem that Russian orphanages in particular seem to be good at producing it in a disproportionate number of their children.
Having adopted from China and gone directly to the orphanage, the Chinese caregivers seem to do the best they can do with what they have, given the high number of children in their care. The people I know that have adopted from Russia speak of filthy orphanages, children underfed, under clothed and left alone for long periods of time. IMHO that’s the difference in situations most of the time in Chinese vs Russian adoptions.