I imagine that the decision came out of a lack of volunteers to host the Book Study™ in their homes.
When we had the Book Study™ at our house, it was ok at first - we didn't have to go anywhere on Book Study™ night and when the kids were small they went to bed early and slept through the meeting. I also liked that it motivated me to give the house a good cleaning beforehand. Unfortunately, there were a few schleps who came to our group and thought nothing of tracking dirt on the freshly washed floor, and ill-mannered children who liked to clog the toilet and made it overflow on a regular basis. It tends to get old quite fast.
We also volunteered to have a Service Arrangement™ at our house on the weekend too. Another round of cleaning got done.
Eventually, we came up with the idea of amalgamating the Book Study™ and Service Arrangement™ on Saturdays - Book Study™ from 9:00 - 9:45 and then Field Service™ immediately thereafter. We had excellent turnouts for Field Service™ as a result. The Circuit Overseer™ didn't like it though and put the skids to it.