How popular was "Cross Draw" in the old west ?
Here's well known Arizona Lawman Texas Jack Slaughter.
He leaned pretty heavy on the Shotgun but carried a Cross-draw Revolver.
It was very popular to wear pistols with the grips facing front and the muzzles to the rear. You see it a lot in period photos. It would seem like a pretty awkward draw, where you twist your hand to point away from your body to draw. You see this typified in the photo of "Wild Bill" Hickok (attached). So this is technically not "cross draw", but somewhat the same style of carry.
Why did they do it? My guess would be that this would be a very comfortable way to carry the popular long barrel black powder revolvers while riding a horse. Barrels of 7.5" were the primary size in the percussion era, and it carried forward in the cartridge era, likely because black powder needs as much barrel as possible to burn because of its slow burn rates. When you get to smokeless powder, shorter barrels can be used effectively.
My older brother was a Colorado State Patrolman starting in the late 1950s (after several years as a city police officer), worked motorcycle patrol and in automobile patrol. Standard issue until the late 1970s was a Colt Python 4" .357 revolver with cross-draw holster. Very comfortable for getting in and out of vehicles, riding the motorcycle, etc.
In his later career working as a plain-clothes investigator he carried a 4" .38 Spl. Smith & Wesson Combat Masterpiece in a cross-draw holster, frequently with a Browning .380 in his pocket. Retired 2001.
Kenneth L. Childress, 1933 - 2018. RIP. Mom was very proud of you and the rest of us miss you.
…You see this typified in the photo of "Wild Bill" Hickok (attached). So this is technically not "cross draw", but somewhat the same style of carry...