Horsecrap. The people in "entrenched positions of gun authority"
ARE doing grappling and merging it with firearms.
This is how I know you are just arguing to try to "win" an argument. If you knew anything about the subject, you'd know how common it is. Heck, even if you just did a simple web search you'd get immediate hits.
The two most common bases for "gun grappling" are BJJ and Judo but there's a smattering of other stuff such as Aikido or FMA.
Here's two super-quick hits that I ran across in the last week or two without even trying.
About the Personal Defense Network | Personal Defense Network
SLAUGHTERING SACRED COWS: ACTUALLY, ANKLE GUNS ARE AWFUL FOR GROUND FIGHTING
Turns out that people "entrenched positions of gun authority" have been merging grappling with gun-handling, professionally, since prior to WWII. Fairbairn, considered one of the Fathers of modern "Combatives" (which includes pistol handling and hand-to-hand) was a Nidan in Judo by 1931 with certificates signed by Kano himself (who would have been 70 at the time).
Your claims are based on incorrect, uninformed, assumption, not fact, are false from the start and easily debunked with a basic google search.