I think it's partly a result of there being more EU countries with good technical education, than with a strong technical employment sector. Something like ~15,

I think it's partly a result of there being more EU countries with good technical education, than with a strong technical employment sector. Something like ~15, maybe more, EU countries are doing a fairly good job training engineers, computer scientists, etc., but only about 7-8 are doing a good job employing them. Hence a tech company in Copenhagen has as a "feeder" not only Danish schools but also to a significant extent Spanish schools, Greek schools, Romanian schools, etc. (If not rectified in some way that will produce other problems, since countries like Greece and Romania are spending a bunch of money to train engineers, many of whom emigrate immediately, going to contribute to the economies of places like Denmark, Germany, or the UK rather than finding a role in the local economy. Some remittances do get sent home, but overall, training another country's workforce probably ends up as a net loss for the training-side countries.)