We've done some speculating on this in the past weeks. The two leading reasons that most think that they jammed the congregation book study are:
1. Elder burnout. The elder ranks are diminishing rapidly. No younger ones are rising up to take control (because college is poisoning their minds and they are leaving the Truth) and the existing elders are too old, too overworked, or a combination of the two.
2. Too much personal research and a willingness to discuss findings at the book study. Some people now realize that the internet has an infinite amount of useful information. They don't hesitate to look things up. What do they find? That "secular" information differs greatly from Watchtower information. So much so that in many cases it is ONLY the Watchtower that believes certain things without evidence. It's not completely unusual for people to bring printouts of stuff they've found on wikipedia to the book study. They're less likely to do this at the Sunday meeting because of the hundreds of eyes.
We don't know for sure why they did it. We don't have any moles on the governing body, unfortunately.
The only thing we can be sure of is that it had nothing to do with the "faithful and discreet slave" being directed by the Jesus.
er