It is for ease and speed of getting into hand, nothing to do with image. They are strapped to leg (as the cowboys did) but that is to ensure rapid release from holster. It also assists in carrying weight of accoutrement belt.
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Possum; AKA:- Ali El-Aziz Mohamed Gundawiathan
Sent from my imperial66 typewriter using carrier pigeon, message sticks and smoke signals.
I would suggest it possibly has more to do with getting in/out and sitting in vehicles. On the hip/belt with arm rests and other design features of modern vehicles would be intolerable and probably contravenes WHS legislation.