Just another way to homogenize things. They did that with the Washtowel studies, making all comments stick with the lesson. They did that at the Theocraptic Misery "School(??)", and they took out the intermission commentaries from the #2 talks (which are now as often read from the Washtowel instead of the Bible). The Public Talks are not allowed to digress from the outline, and they are now very strict about that.
Now, I guess they had to go after the one remaining loose end. Shortening the book study allows them to control such left-field comments. It also prevents those fun nights after.
And I bet they are going to start making field circus on those former book study nights mandatory. If you are not out in field circus that evening, it counts as missing a boasting session and you will expect a call from Brother Hounder. That way, there will be no more excuses for going irregular or inactive.