Brake cooling schedule is a calculation for turnarounds, to give an indication of the minimum turnaround time - or leave the gear down for takeoff (performance penalty). On days with multiple sectors and short turnarounds, the overall temperature can still slowly rise as there isn't really time to let the brakes cool down. As the day progresses, every time you do a turnaround, the risk of running into a "minimum turnaround time" (or takeoff performance penalty due to gear down requirement) is bigger and bigger. Think hot 4/5 sector day with very short flights, extended taxi time, high payloads,....
In order to provide extra cooling to the brakes, Boeing proposes to lower the gear earlier on the sectors. The advantage is that your starting point in the brake cooling schedule calculation will be lower, hence less chance to end up with a turnaround time requirement (or gear down required after takeoff) after sector 3/4/....