In the beginning…
Colt SAA (Model 1873 Single Action Army) revolver in .45 caliber was adopted by U.S. Army in 1873.
Shortly thereafter, the S&W Schofield was also adopted by U.S. Army, and while Schofield ammo would work in the Colt, the opposite was not possbile (due to shorter length of S&W cylinder as I recall). Hence the Army decided to adopt the shorter S&W style round so it could be used in both types, simplifying logistics. Apparently this short length was military standard until the SAA was finally withdrawn from service (even though the S&W had been retired after only a few y ears in service.
Dissatisfaction with the puny stopping power of the .38 caliber revolvers (Colt made Models 1892-1903 series, mainly) led to the adoption of the .45 caliber Model 1909 revolver (basically the Colt New Service Model). With no S&W Schofields around to complicate things, the .45 caliber revolver cartridge Model of 1909 was adopted to go with the 1909 revolvers, and I believe these used the “normal” commercial length cases, not the previous military dual purpose “shorter” case.
THe Model 1909 revolver remained in use for many years after adoption of the Model 1911 .45 automatic, as it took a while to procure enough to meet all the needs of active and reserve forces, and older arms tended to be kept for war reserve stocks even when obsolescent.