I will not venture to say why the great archers are longbow shooters,but will add my personal thoughts.
I am a relative newbie to traditional archery, having been hooked for about 7 years now. I started out with recurves, a Red Wing Hunter, then several different Bear bows. I love the history of Bear Archery, and the looks of Bear bows. I own several of them, and am always looking for a deal on a good one.
That said, I have 2 bows on my rack that are the ones I truly love to shoot. When my Thunderstick longbow is in my hand, it is part of me.
I love the feel of the grip in my hand, and the smell of the leather grip. It is feather light, whisper quiet, and smooth to shoot. It is simplistic archery. Stick and string, hand and eye.
I still shoot most of my recurves, but I do not truly lock on with anything but my longbow.