...if "government decisions" equate to "logic". Ever.
A standard duty sidearm is normally a full-sized, full weight pistol. The Beretta adopted as the M9 comes to mind.
For law enforcement or security work, the standards are a bit different. For instance, In the early 90s, U. S. Customs decided to replace the issue sidearm - then a Smith & Wesson 685 called a 'CS-1' - with the S&W 6946, a cut down 9x19 pistol made for concealed carry. The original idea was this pistol would be issued to all troops, uniformed and plain clothes alike. (Then, the Service allowed the plain clothes agents to carry non-issued weapons and the uniforms were stuck with the short and wide gripped 6946s.)
Historically, military air forces carry smaller, lighter guns. I think - not for sure - the reason was to keep weight to a minimum. (For instance the Italian Air Force's 1935 Beretta in .32 ACP and the U. S. 'Aircrewman' revolver made of aluminum and chambered in .38 Special.)
Logic? I think it's more along the lines of someone is assigned to decide and a particular firearm is selected based on whatever criteria that 'someone' decides. Then whoever offers the suitable item at the cheapest price gets the deal.