Do teachers generally refer to hard-to-comprehend books? I have studied at 4 universities, and in 3 different programs.
I always observed that when asked for a recommendation for a  book to understand a topic easily and clearly, university-professors always referred to books that are not student-friendly, i.e. written for more advanced level than that of the student. Then, after several years, I discovered that there were easier-to-comprehend books available which could have helped me acquire better grades.
Is this intentional?
If Yes, why?
If No, is there anything wrong with the higher education culture of the country I am studying in?
One possible reason is that I feel the style of textbooks have changed in the last years, so that newer books are sometimes easier to understand (use more modern-day language and symbols, is friendlier to the reader etc.) (This does not necessarily imply that they don't cover as much details as the older ones or are more superficial)
But the professor, being older, does maybe not know about them or is used to the older style. And often, some old books are considered classics that all students should know regardless of whether something better came out in the recent years.
Additionally, another reason might be that your professors don't have any education in teaching and don't know much about it. Most of my professors thought the most effective way of teaching is to copy lecture notes onto the blackboard and read it out loud with a monotone voice, without any explanations or motivation because they assumed that having it written down means students know it. Those may also be the types of professors who recommend you a hard-to-read, but factually correct book.