Yeah there are MAJOR reasons that a huge amount of Chinese scientists immigrate to the US every year, but almost no US scientists immigrate to China.
These are smart people, they’re not going to make major life decisions based on simplistic takes from political opportunists.
US has/had the best schools in the world. US provides/provided remarkable academic independence (tenure, etc). US provides/provided the best expected economic return to foreign scientists.
As we dismantle those components via xenophobia, anti-intellectualism, funding cuts, and so on, trends will change. Already I see a substantial uptick in my PhD/Academic friends moving to Europe as we cede our historic advantages.
If, in say 15 years, China provides better schools, or better economic returns, or (perhaps unlikely) better independence, or all 3, then scientists will go there.
The reason is money. The US has the world reserve currency which basically means infinite money. This will soon end and China will have the world reserve currency.