I could see that the appeal of Ireland can be increasing and Poland sounds cool. I'm not saying that the USA is great, it has tons of problems.
UK numbers yes, though maybe gloomy weather plays a role? Just kidding. That said, Brits are slightly more likely to move to Spain than US despite it being a tiny country in comparison and not necessarily easier to move to after Brexit.
Spain, not sure. It’s tricky to compare since non immigrant Spanish speaking population in US is probably significantly lower than Spaniards speaking English. But yeah, you probably have a point on that one.
Spain’s entire population is 48 million.
I have never met an American that migrated to Spain.