I can think of a few reasons:
In many European countries, the five-year master's is still seen as the primary undergraduate degree, at least in universities. (There may be other more applied institutes with shorter degrees.) When most students are expected to graduate with a master's instead of bachelor's, the program is likely to be more theoretical.
Elite schools are a foreign concept in many European countries. In such countries, ambitious students motivated by status and success are more likely to pursue a professional degree such as law, medicine, or business. The ones that choose an academic program such as CS are more likely to be motivated by the subject matter itself.
You don't see a representative sample of European graduates. Moving to another country requires huge sacrifices. Most people from wealthy countries are unwilling to make those sacrifices simply to get a better job. Those that do emigrate for work tend to be more career-oriented than the average.