Changing from DA to SA and be able to control shot placement took more training than a pistol should take, especially since a pistol is a secondary weapon designed to help you get to the battle rifle. The Beretta was a poor choice.
The SIG is a departure from the one-size-fits-all to a true modular system that can be modified for the mission. Optic, lights, lasers, suppressors, all can be fitted to the basic frame and slide assembly and not change the operations one iota except in capability.
While I prefer a 1911(and carry one every day), I am envious of the M17/M18 platform and it's versatility.
Glock was upset it was not chosen, but it did not, and does not offer any of the configureability the SIG does.
Had an uncle that was drafted at the end of WWII. He ended up as an MP in West Germany someplace.
They were issued extremely worn 1911s that were in dire need of refurbishing. Those 1911s were a problem during qualification at the range.
The configurability of the Sig320/M17/M18 is not so much the attachments as being able to use the same receiver in different size frames and for different calibers, to satisfy the needs of small handed female MP’s and guerilla handed SF operators alike. It maintains a flexible but consistent set of supply parts to maintain across the force. An advantage for the military.
On the street, there isnt much cost savings between having the parts to swap out on a single P320 or just having multiple guns.