During the middle 1890's the Winchester model 1895, chambered in .30 Govt. (30-40 Krag) became popular with lawmen in Texas, New Mexico and Arizona. The ammunition was often carried in wide 3 to 3 1/2 inch belts with two lengths of cartridge loops. The lower ones were smaller, to prevent the bottlenecked cartridges from slipping out.
But a problem arose. The belts were so wide that holsters (called “scabbards”) couldn’t be slipped onto them. Someone, possibly Texas Ranger Capt. Hughes, got the idea of cutting a slot through the middle of the belt that was wide enough to slip the skirt of the scabbard through. This did not substantially lower the holster though.
The drop-loop rigs that were later used in movies date from the middle 1920’s, and were indeed invented in Hollywood.