It can also be more fun to be forced to wait and read along with the class. You get to take part properly in predicting what will happen to which character, based on what was in the text before that, not what came after. And although that’s something you naturally do as a reader, pausing and doing it deliberately can teach you a lot about writing.
Obviously it is difficult to do, if you really like a book. But it’s not an arbitrary rule designed to punish fast readers.
Though one time - while on a PGCE (postgraduate teaching course) - my tutor outright said I was lying when I predicted everything about a short film we were watching (he paused partway through), and I said I hadn’t seen it before. It was some obscure French short film and just not the sort of thing you happen on by chance, especially if you don’t speak French. I just watch a lot of movies and TV and it’s not hard to spot patterns and make predictions.
He was really annoyed with me. He also marked me down during a lesson observation for not gesticulating enough with both arms. One arm was broken and in a cast and sling at the time, having been broken by a student. When I pointed that out, he stuck to his guns. I actually gesticulate quite a lot, but not when one arm is strapped to my chest!
There’s another couple of weirdest things, I guess!