Probably, a significant reason for the current brain drain in US is that a large portion, maybe even majority of really smart students there choose to take courses that will position them well in the FIRE (finance, insurance & real estate), consulting services and Wall Street sectors.US itself is having its own brain drain. Not just lower appeal for new immigrants and transfer students, but there is also the decreasing birth rate, and Americans themselves moving out to work elsewhere.
Starting pays in Wall Street for top graduates are mind boggling, a fresh MBA from a top school but with zero working experience can easily ask for $120k or more p.a.. Law, actuary, accountancy, financial courses offer an arguably easier path to a comfortable life. STEM graduates on the other hand have also been heavily poached by Wall Street for decades.
China also has such issues but likely to a lesser extent.