I’ve wondered this too (not that I’ve even contemplated tying a tarpon fly). Thanks for the backstory!Before Flourocarbon, and when anglers used to use a wire "tippet" section, many anglers would snell the flies to their wire tippet. Some still do this with mono, but it is becoming more rare.
Additionally, the older flies used saddle feathers, which foul easier when tied up at the front of the shank. So tying materials in at the back only is also to help prevent fouling.