The truth is it is a lot more complicated than you make it sound. There are some schools which are relatively young and focus on coding. Historically they were

The truth is it is a lot more complicated than you make it sound. There are some schools which are relatively young and focus on coding. Historically they were expensive (for French schools), even though one of them is now free thanks to the generosity of a French billionaire. They recruit students with different profiles than the traditional "Grandes Écoles" and they get much less recognition from French employers, especially large companies. Because of that, their top students may indeed be inclined to move abroad, where degrees matter less. In the more generalist, traditional engineering Grandes Écoles, however, the phenomenon is a lot less prevalent. Some students do move abroad, but my experience is that it is not correlated to their competence. Those with propensity to found companies are more likely to go to the US, but that is mostly because the ecosystem there is like no other. On the other hand, you may have noticed that some large US companies (Google, Facebook...) have been opening research labs in Paris, while top French companies such as Criteo send their marketing department to the US but keep development in France. This is not only because talent is cheaper (others have already explained how low salaries for not mean low costs) but also because top technical talent doesn't necessarily want to emigrate. This is cliché, but Fabrice Bellard is still living in France, and Yann Le Cun moved back. :)