Comment by roenxi

That isn't a justification; if the students think that it helps they can take notes of their own initiative; handing out a copy of the slides doesn't disadvantage anyone. The lecturers are just making a petty power play because they want to feel important standing in front of a bunch of eager young students

There simply isn't any pedagogical justification for withholding information post-lecture that was deemed important enough to be included in a lecture. Everyone knows this material is critical to understanding the course. If professors want simple optimisations to help students learn then they would be doing something like organising lecture material to promote spaced repetition.