>> I wonder if there are strategic reasons behind this - do the US and European countries fear a growing China and India and feel the need to compete, for example?

Well the US would be in a slow decline if not for immigration, so we're trying to get smart people to come here which both sustains us and deprives the others of talent. We also seem to like ambitious folks willing to work hard for less pay, so we maintain a very leaky southern border.

China is the only country I know actively trying to address population. The guy who invented RISUG is in India, but I haven't checked how that's going in a while.

I always had a feeling that most of China's "success" is just centralizing wealth of the whole country in a few places under governance of not so many people. With so many people you don't have to be terribly successful at reform to produce a bunch of impressive cities etc. Per capita it has a long way to go. We'll never know until/if China breakups into multiple countries (or something similar).