There is a fairly long history to Western holsters. The rigs changed over time, and also depending on the regional influences, the holsters/rigs could look decidedly different. Also, a lot of the rigs made today are for Single Action Shooting competitions. Whereas holsters I make, are for daily carry either inside or outside waistband, hanging on a daily worn belt. A complete belt/holster rig wouldn't be practical for me, as they tend to ride much lower than a standard belt holster. Also, different guns would require a different complete rig for everything you might carry. One more thing...today we are likely to carry numerous guns for different occasions, while in the 'ol days, they likely had one rig for their one, (or two) guns.
Jeff