Because saltwater rods are used from boats... Wading rods are long.
A 6' rod with a typical short handle has limited mechanical advantage on the reel end... virtually none and the strain is taken at the wrist. Increase the handle modestly and allow the butt to be pressed to gut and the game changes.
Make the rod longer and the handle will also be longer to aid all of the things done with longer rods... Like fighting fish... and the game changes again. Moving fish away from obstructions and toward the beach or net is far more important than how much actual force you might have to apply.
Your mechanical advantage point is real, but like lots of things in the real World it is not the whole picture. Your example of Lee Wulf doing it is noteworthy BECAUSE he went against the obvious mainstream opinion and direct knowledge.
Try to maintain 10# of pull on an anchored gauge with a fly rod... You will be lucky to get close to it and staying there will be problematic. It is not all about how hard you have to pull with a fly rod as very little force is truly applied.
Grayling's jack argument is obviously flawed...
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