It's big. It's a baitfish. It's a big, bad, baitfish that all predatory fish love. Works best wherever big fish eat little fish.
Having a selection of general-purpose flies that work for a large range of species and cover the most number of fisheries makes a lot of sense. The broad profile stands out well in deeper saltwater fisheries, and have proven very successful for Striper, dorado, roosterfish, snook, and tarpon in particular.