The US has the best research universities in part because it's socially accepted, even expected, to call anything remotely good "the best" over here. People are a bit more restrained elsewhere. For universities, they're admittedly the best by several objective measures too, but the willingness for self-promotion helps :)
Again...personal experience but I can speak to this a bit. I went to an undergraduate university that would be wouldn't be considered highly ranked, but was nationally known in one subfield. I remember being surprised at one point to see a number of articles in major science media sources from MIT about a 'breakthrough'. I read the articles and they were 100% describing something that we did on a regular basis in und…
It's a bit like an article circa 2006 about the awesome strength of the US stock market.