This began to change with the advent of the "armored" division, where tanks and personnel carriers were married to the grunts. Culminating in "mobility" warfare late in the 20th century. Along with the introduction of improved BA, the fighting load out changed to something easier to wear while "mounted" in vehicles. And packs became largely just luggage in the vehicles.
Perhaps in your (horse) Cavalry units before they were forcibly converted to steel?
Same same M1903A3 rifle but way different webbing. Specialist pouches for BAR.