Get rid of the BS and they are in control again.
I think that's it, but in a different way.
With the slow down in brothers reaching out, they had less and less company men to rely on to lead the bookstudy. This would allow people with thoughts not in line with WT think to be able to speak more openly. They could ask questions, raise doubts. In fact, if allowed to stray from the WT program because of questions raised, the book study could actually become a real Bible study group instead of a WT book review group.
To curtail this, they needed to make sure the groups adhered to a strict set of rules on how the progam was to be handled. In a relaxed atmosphere of someone's living room it was too hard to enforce those rules...but at the KH people were more willing to follow the rules with fewer company men needed to make sure things were kept in line with the Society's program.
Kill the book study, make em all come to the hall with one study for the entire congregation and they are in control again.