I wonder if this is to make things easier for Circuit Overseers to be drawn, eventually, entirely from the ranks of working Elders, who would serve just a few weeks a year, a good number being Appointed to cover each Circuit.
That would free up any Circuit apartments that they use, (I know this is far from every Circuit that has one, but many do) and save on Company Cars etc. meaning more money available for direct donation to the W.T.
The main advantage in using working Elders is that it distances the W.T itself from any Legal liability should more Paedophilia cases come to light.
The WT is all about the $$$.