But here's the thing; the WORST score for the USA in the metric used was the proportion of
foreign contributors to the scientific output and of
foreign students in tertiary education. So the SMALLEST contributor to the ranking of the USA was the foreign scientists that helped produce science. This means that although Canadian, UK, Swedish, German, or other nationality scientists may want to go get paid in America,
they are making a smaller difference in the output of the science in the USA than foreign nationals are making in their own countries!
Heck, even the proportion of international students in 3rd ed in the USA is in that metric so this means that, as compared to the other countries in this study, the USA has a very low proportion of international students in science courses and a very low proportion of international contributors to its research.
Look in the link to the study in my GP post. Under point 2.3 is the definition of their "Connectivity" metric and under point 3.3 it explains the USA's low reliance on international collaboration in research.
The United States, Korea and Japan are in the
bottom quartile for [international] research collaboration, in part reflecting the existence of a critical mass within
the national research community.