I wonder if it has to do with the fact that with a compound, one is holding a fraction of the draw weight at full draw and with a recurve you have it all?Never ceases to amaze me how much compound grips have evolved but single string grips are stuck in the age of rounded of 2x4s.
I always used a finger sling with a Flatbow. Maybe not with an ELB but certainly with an AFB.For us longbow shooters who can't really use a sling, I wonder if a small O-ring on the back side of the riser would help as a "locator" for the index finger? I don't want a full grip, but I can't shoot open handed without losing the bow. This way, I can curl my fingers around the grip and get the same position every time.