I would think a restriction in the US compared to e.g. Europe is that many people in the US hold on to a particular job due to the health insurance they have at

I would think a restriction in the US compared to e.g. Europe is that many people in the US hold on to a particular job due to the health insurance they have at that particular job. A second issue is mortgages. While that is a problem in many European countries as well, some countries like Germany have a much higher portion of the population renting. Moving is thus much less of an economic risk, as you don't have the potential problem of moving from an area with economic depression where you can't sell your house without a big loss.