@ No Room For George who said,
"I don't know why all of you have to always assume the negative when it comes to the direction given by the WT. The reality is that, the Book Study at its former setting wasn't effective in strengthening Christian families which is the nucleus of a stable Christian Congregation [...] That way there was an opening for the Family Worship Night arrangement without it becoming too burdensome upon the sheep."
Do you believe every reason the Societ gives for making a change? For decades we were told that every family member should have his personal subscription the both magazines because it was important for his spirituality and development. What did the Society say when the subs were discontinued? That 'it's for your spiritual benefit, since it will give you one more good reason to get to meetings, to get your magazines'! Do you believe that one too?
@ the OP.
Maybe C (liability issues), although all the choices make some sense. The book study was in my home for many years, and that little contribution box never had any money in it. It was the least-donated-to meeting of the five. If there were any liability issues at all, the book study was losing money, and that alone would be reason enough to cut it from the program. Any business corporation would do that.
"...real reason behind this decision (the great tribulation was about to start...etc.)"
The reason the book study was started in the first place (small groups, meeting in private homes) was to prepare for the tribulation. The idea was that when the government moved against JWs, and closed KHs, there would still be a way of having organized meetings.
It's amazing how all the Society's good reasons keep changing.