I don't have time to read all these wonderful comments. I just wanted to make sure this is covered- this is purely a money thing.
Dropping an entire day each year (the SAD) frees assembly halls. Having two circuit assemblies a weekend allows the "Branch Visitor" (or whatever he was called) to just make one trip to Dirtweed, Montana and cover two groups with the same talk.
They will mind-control suggest that the savings on hotels should be put in the box.
All those freed up days will allow more Regional Conventions to be held in assembly halls. They hate renting out facilities for three days. It was either go to two days or get more stuff in assembly halls. They still might drop to two-day conventions.