Where do you propose regularly finding hundreds of millions of skilled English speakers of similar values who are interested in permanently migrating to what will be countries clearly in decline?
Even India's fertility rate is now below replacement, and they're increasingly actively working to turn the tide on their brain drain. And India's economy is both already massive and growing quite rapidly. At current trends they'll pass the US within a decade or two. They certainly aren't just this long term sustainable pool of people to draw from.