This was the point I made earlier. Consider Richard Feynman lectures. Why didn't universities collectively took the decision to create pre-made/cooked lecture videos for topics that don't change and show these videos during normal lecture which otherwise would be the job of professor to revise / prepare the topics the night before and deliver. The professor spends so much time in doing the same thing again and again everyyear. This would have freed them to have more discussion, office hours and so on.