9x19 Parabellum is the bestest thing ever and therefore all other cartridges are "a solution in search of a problem" so don't bother trying to innovate or offer anything new/interesting, just chamber everything under the sun in 9mm.
Honestly, I'm waiting for someone to show of a Lever Action Rifle chambered in 9mm Parabellum because apparently no other cartridge needs to exist anymore. It's so incredibly dull, but the market has become so stagnant that even when ammo companies attempt to introduce a new pistol cartridge, how do they market it? ".30 Super Carry! It's like 9mm, only smaller so you can fit like 2 more in a magazine! Huh? Huh? That's compelling, isn't it?"
It's enough to make me want to buy a 5.7x28 Pistol just to support something other than 9mm. It's like, okay, it's a good defensive round, but variety is the spice of life and the market has gotten remarkably dull. I wish that .357 SIG would get a push, as I think it has untapped marketing potential, and I've seen an increasing number of GunTubers pushing it over the past couple of years, so I think it's due for a revival.
One could use as a parallel the .222 Rem. Mag, a vastly superior cartridge to the .223 Rem but with cheap ammo and once fired brass free just for picking them off the ground the .222 Mag was doomed.
With the cheap ammo and tons of once fired brass the 9mm is not going to get any less popular very soon and I saw it go from just an oddball military surplus cartridge that was used with corrosive surplus ammo in the 50's to the superstar it is today, especially after Law Enforcement went over to the high cap 9mm craze that made the .38 special look like an extinct dinosaur even though the .38 special is actually the more powerful cartridge.
So it begs the question how was the .38 Colt (Father of the 38 Special) such a dismal failure during the Philippine fight for independence from the U.S. in 1899? In fact it was not any more a failure in the field than the .45 Long Colt or .45 acp was because the Troops complained about all 3 calibers. The .38 Colt failed only in the propaganda of the bull crapping Gun Writers of the day and accepted as fact today and still repeated (just last month) by self-anointed gun writers.
Both Col Thompson tests (which he hid from the Ordnance Board and from Jan Libourel who researched "real" U.S. Army records proved that smaller cartridges like the 9x19, 38 Colt, and .30 Luger killed 1,200 Steers ever bit as well as the big bore revolver cartridges. When Co. Thompson did not prove his big bore theory he then in a blind panic cheated in the tests and ran out and bought expanding bullets for the big bore cartridges (which he said did expand) but again they still killed no better, a fact he hid from the Ordnance Board who never bothered to do their own testing.
Moral of the story, most gun writers are as reliable and knowledgeable and honest as most used car salesmen and we all know a used car salesman would never lie to you don't we!!!
As far as the 38 Sig, admittedly it is more powerful (but holds less rounds in the magazine and recoils more and has more muzzle blast) but brass and ammo are way more expensive and it has a very short neck making it a pain to handload for and even factory ammo does not grip the bullet as well as the 9mm does nor does the .38 Sig line up the bullet in the chamber as well as the 9mm either. Now admittedly most people are not skilled enough shooters nor are most combat handguns built with the accuracy of say a match grade 1911 so the difference in accuracy goes unnoticed by Jethro Bodine when he is blasting tin cans on the Lower Forty Acres while he is knee deep in brass and still shooting fast. Occasionally he even hits a tin can.
In conclusion there have been many ballistically superior cartridges that just never made it and for a variety of reasons and Jethro is none the wiser nor does he wish to be either. To Jethro if the Service uses it or Law Enforcement use the cartridge therefore it must be the best to use, it never occurs to Jethro to do any research or testing himself. If Jethro did, he would have found the .32 acp superior to the .380 and the 9x19 superior to the .45 acp, and the .38 special superior to the 9mm but those are more stories for another day and time and history has validated it all it's just that Jethro flunked ballistics and history classes.