Weapons produced for the "military" usually have an edge, since they're produced in such high numbers, and at the end of the conflict, many of them are sold on the "surplus" market, squeezing purpose-built civilian designs.
When WWII ended, there were millions of 98-design Mausers that came home with GI's, or appeared in the surplus arena. They were re chambered, and "customized", at a cost less than that of a new Winchester or Remington. The Springfield 03, and the Remington/S-C 03-A3 both made their way to the civilian market when surpassed by the Garand. The action makes a great conversion, and un-rechambered, the .30-06 is available everywhere.
Millions of 1911 pistols survived both the Great War and WWII, and many of those ended up in the civilian market much less expensive than commercially produced Colts. Now, whether they could hit the broad side of a barn with a loosey-goosey 1911 was something else.
There's also the reverse. When the U.S. couldn't produce enough 1911's in the Great War, Colt and S&W both modified existing revolvers to chamber .45 ACP, and those were later sold on the surplus market. The Colt New Service languished because the U.S. Army adopted the 1911, making the New Service in .45 Colt, instantly obsolete. It got a second life when adopted as the Model 1917.
There's also the aura of the durability of the produced-for-the-military weapon. M1 Garands are brutally tough; over-engineered to last through combat. However, a civilian version probably wouldn't need all the excess wood and metal the military required. And there's also the nostalgia factor. People want/wanted the rifle of the "Greatest Generation".
The Mauser 98 was a great design, military needs aside. It's still the basis for many commercial rifles, and simply hasn't been surpassed. Lot's of high-pressure, magnum cartridges have been chambered in a 116-year-old design, as well as standard chamberings. Hard to beat the design.
The AR platform was well along in its design and improvement when the Mini 14 was introduced. While the Mini 14 has developed a following, the AR platforms really rule the roost. The "look" has a lot to do with the acceptance, and companies have made billions in add-ons alone. Never mind the customization of the platform with caliber changes, and system improvements. A lot of those civilian improvements have "back flowed" to the military. Sights, ergonomic changes in stocks, etc. all started out in the civilian market.
The Beretta 92 platform was mature when it was adopted by the U.S. military. That, in itself gives it cachet with the civilian market.
There is also the Thompson SMG. It came along too late to be used in the Great War. However, it was marketed to civilians, and it developed a reputation in part, because of the Prohibition crime surge. It's original purpose did get re-ignited when the military needed a SMG during WWII, and the design was modified to make it more usable for combat.
As the modern battle rifle has evolved, only the AR15 has evolved in mass numbers. The M14/M1A platform has a relatively small following, but has also been revived in the military. It wasn't in use long enough to provide penetration into the civilian market in the numbers that the M1 Garand has. It was also originally a selector-fired rifle, and that made it nearly impossible to purchase in the surplus market.
The Colt SAA-S&W #3 is an odd rivalry. While the S&W had some tactical advantages, such as fast reloading, the politics of the Army's procurement operations made the difference. Major Schofield got a small royalty on the guns sold to the Army (conflict of interest). And S&W probably grew tired of paying the Major. There were also reports that got back to the Ordnance Bureau that stated that the S&W wasn't as sturdy, owing to its top break design and ratcheting system. There was also the issue of ammunition interchangeability. You could chamber .45 Schofield in your SAA, but not the reverse. You could see a lot of S&W #3's on the "frontier", and they were popular. Most people carried them a lot, and shot them little. So, not as many wear problems. But the SAA was what the Army used, and I'm sure a lot of folks bought SAA's because of that. I've read stories (anecdotal), that the Army would supply .45 Colt ammo, as well as .45-70 rifle ammo to buffalo hunters. The .45-70 cartridge was an effective cartridge on bison. The politics of supplying ammo to bison hunters is another story in itself.
It's a great discussion, and sometimes evolves into "chicken v. egg".
