a) If someone is attracted to the West, they will not be available to work in the Chinese or Russian economies.
b) Some of those people might be Russian or Chinese, and so if the West can attract them, this is a loss for them (ignoring the value of bridges).
So, both Russian and China have an interest to support political movements in the West which want to erect barriers to attracting international talent.
(Beyond that, safe to say that there are at least one or two other things going on at the same time. Maybe three.)