Germany and Scandinavia come in a distant second, with Southern Europe falling significantly behind. The disparity in IT-intensive industries is particularly large.[2]

This is true even when comparing the productivity of workforces within the same market. I.e. European who work for American multinationals tend to be more productive than those who work for local multinationals. The short answer is that American management culture is really world-class. And, I think in software in particular, good management is a major force multiplier in terms of output and execution.

[1] https://www.aeaweb.org/articles?id=10.1257/jep.24.1.203

[2] https://www.aeaweb.org/articles?id=10.1257/aer.102.1.167