We don't know why the search area was extended. It could be because the search is going faster than expected (weather may have been better) or because some debris may have been spotted....
Patience is the virtue..... The fact that this 3rd search happens is great, and the commitment of those involved, despite all the criticasters on this forum, may well lead to a fourth and/or fifth search....
I am humbled by the diligence of mm43 and other including the search party organizers.....