> to that end, i'm not sure why it exists, except that it's truly a unique style.

Many people swim as a form of exercise. Fly is exercising different muscles and allows me to get my heart rate up higher than freestyle

Fly is useful to train for other strokes

Perhaps more importantly, I think that having a different stroke to do makes swimming more interesting. Whether doing sets as part of a swim team or on your own, it's more interesting when you can vary things. The more swimming is interesting, the easier it is to enjoy and keep doing it