possibly for ease of movement, allowing the fabric in the large pleat to open out and the apron to stay over the under apron rather than being dragged sideways when you sit - or vault gates or step over a railing or low wall

I wear a kilt as part of my Morris kit and they get some wear, so the last one has no sewing in the fell at all, it all just hangs from the waistband - yes it flies, but I also wear black leggings so not a problem. When I sit down with the band the aprons fall straight down and don't get into fights with the bellows of the melodeon, which can cause havoc with the timing.

The reverse Kingussie style helps to keep it in some sort of order when I stand up again.