As an example ETH Zurich, which is arguably one of the best universities in Europe, still educates Bachelor's students in German:
Please note: the Bachelor’s degree programmes begin in German. In the second and third years of the programmes, some of the courses may take place in English.
This doesn't make sense to me as it's obvious that the vast majority of technical literature and textbooks are published in English. And pretty much every major scientific journal only accepts works in the English language. This also decreases the amount of competition between the applicants as German speakers hold an advantage over others (not to say native English speakers don't hold the same advantage back at home, but English is by far more common).
So why didn't every single major university switch to English already?
EDIT: I am mainly referring to programs in the STEM field, such as engineering