Simply put, today's students do not get much out of long lectures, no matter how well they are constructed. The material comes too fast and does not sink in well. The students of the past responded by becoming quiet scribes. Today's students demand more action and accountability. They do not read their texts.
Some students even disrupt lectures.
I would have bright and eager students. It is the lecture method of teaching that is impossible -the method of teaching via long lectures is crumbling under its own weight. This is true not just in mathematics. Across the University of Illinois, there is a major controversy about whether professional notetakers may take notes and sell them to students who would rather not attend lectures. We had a second chance when the Xerox machine was invented, but we muffed it.