I have a G21, full size railroad tie with trigger, and can attest to an oversize grip, and not the ideal grip angle... Even with large hands. However, the darn thing always goes bang, regardless of ammo. So I keep it as a holstered "go to work" sidearm in a milsurp gas mask bag.
Perhaps its a marketing issue for other companies. The bread and butter of S&W, Wilson, Para, Ruger, etc,.. are retail civilian sales. As opposed to HK.
Given the parameters of the military, that eliminates a few manufacturers not interested in large scale issue. I know the Spec Ops folks can choose literally whatever they want, and should be able to do so, I just was wondering why S&W, Wilson Combat, Kimber, Para, Ruger, etc,... may not have tried to get the M9 replaced with say a .45 caliber.
If its cost,...I wonder, as our gov't often has no issue with cost....Seems toilet seats, and hammers, were given no rationale to cost,....HK is proud of their stuff. I can't imagine the cost per pistol is that good.