>note that we are not seeing net migration of high-pay tech workers from the U.S. to Europe that we should if that were true.

How many EU's are migrating to the US?

Most people's solutions in first world countries is not to go through the arduous process of finding work in another country and leaving behind their entire culture and network behind in hopes of a better life. That is not the same decision you make as if you're jumping to another state/province (which in itself is already a big life change).