Two really poor examples that don't form a rule.
The Russians adopted the M1895 Nagant revolver because it was cheap and they already had a working relationship with Emile Nagant from the M1891 rifle contract. The Nagants were the lowest bidding contractors. The Russians also went out of their way to make the gun trials as complicated as possible. For one, the Russians required the test guns to have a manual ejector like a Colt SAA. In the 1890s. When the C96 came out the next year. Sweden and Switzerland had also already adopted the M1887 Nagant.
The M1 Carbine was a PDW. It wasn't used like a rifle. It wasn't intended to be used by frontline infantry, although guys like paratroopers used them because try jumping with a Garand and the folding stock Garands sucked. A cook or a trucker was better off with a bigger mag of easier to shoot ammo than eight rounds of .30-06. Putting a carbine in the hands of a trucker means one more Garand available for troops on the frontline.
Caliber wars certainly did exist at the time but were not as relevant in pocket pistols because of bullet technology - you would've been carrying FMJ at the time and your options were .25ACP for deep concealment, .32ACP as a backup gun, or .380ACP as the biggest option. The 1911 and Webleys in .455 are examples of caliber wars. The US used .38 Colt New Services in the Spanish American War and loved them so much that they demanded a .45-caliber semi-auto, which evolved into the 1911. The Brits never had an interest in anything below .45" until WW1 - if you look at early Webley semi-auto pistols, they were all developed in .455 Webley Auto because the Brits had no intention of dropping down to .38/.355 caliber.
Even 9x19 is the result of a caliber war. The Swiss adopted the Luger in 7.65x21 but the Germans simply didn't want such a small bore diameter handgun. So Georg Luger developed 9x19 from 7.65x21 and the result is the most popular handgun round... ever?