I had the impression that they ended the weekly book study because they realized that the meeting schedule was onerous and might wear people out. The thing was, it was the most convenient of the meetings for most people- the location was usually closer to home than the Kingdom Hall, it was only an hour, and it was a small and cozy group. They let us host it at our apartment for many years, which made it even more convenient.
But if the WTS was going to shorten the schedule, they couldn't cut either of the big meetings. So they axed the one that was probably the most popular, while still using people's apartments as a staging location for field service. They used my apartment for a few years even after I faded, because my mother is a diehard PIMI and I wasn't causing any trouble and I think they were hoping to get me to go back in.