Auto-sort is intended for a multi-lap race such as a mile run. As each runner completes a lap, they are moved to the bottom of the active group. Therefore, as the group finishes their first lap, the person now at the top of the list is the one who finished the first lap the fastest and is thus likely to finish the second lap at or near the top. Thus it makes it easier to find each person.
Similarly at the end, as you hit Stop for each runner, they go to the bottom of the entire race. While this doesn't help on the first lap, prior to the race, you can manually sort the watches in the anticipated order (just press and hold for a moment until the watch comes free of the background and drag it whereever you want).