My 2 bits, .357sig caliber......
I've been around firearms & the shooting sports industry since the early 1980s. I also served four years on active duty in the US armed forces.
I'd opine that the main reasons why the .357sig didn't really take off or gain support was due to these factors;
SIG Sauer; The high end firm designed the round to work like a semi auto .357magnum. It pushed the new pistol round for it's own models(P229, P226, etc) but it couldn't really compete with the S&W .40 which came out to wide support in 1990.
US law enforcement/armed citizens; The .357sig round started off at the end of the mid size/high power level pistol caliber race. Several mid size rounds like the 9x23, the .41AE, the .356TSW etc came & went. Many PDs & armed citizens either "moved up" to a .45acp or picked the new .40S&W.
Firearm selection: Few US gun makers really warmed up to the .357sig other than SIG Sauer. Small firms may have a few models but the larger outfits like Glock or S&W just stock them to keep agency sales happy or for the small # of public sector .357sig shooters to purchase.
I like the .357sig & would carry a .357sig semi auto on or off duty but I can see how/why the .40 & .45acp are more popular.