probably because they're bored. Giving a live lecture is the most disdainful form of teaching, using the slowest and most unbalanced way of passing info.
Video your lecture so that the students can watch it at 1.5x speed and do exercises during the class time so that the students are engaged if they decide to show up (which they are more likely to do if they don't have to sit through your live presentation at 1.0x speed).
They'll adjust.
The students won't watch the recorded videos or do the readings. That's why we have to lecture live.
Then even if we get great students that will do the readings and watch the videos so we can do a flipped classroom; the students will complain that they had to teach themselves and tank the student evaluation scores compared to the lecture version.
Students expect lectures and dislike more active forms of learning even if they learn more. This is not their fault as it's what they've been trained to expect from K-12.
He was surprised nobody wanted to attend his lectures.
EDIT: fixed a lot of typos...