I have an alternate theory as to why the Army had to go with something other than Glock. When GEN Milley was FORSCOM CG, he made a comment that he could solve the handgun situation just by buying Glock 19s with a GPC. Then the Modular Handgun System goes for testing after GEN Milley becam Chief of Staff. So his previous comments would make selecting the Glock look like GEN Milley had influenced the process unduly, and probably would have resulted in lawsuits by all the other submitting companies.
It's hard for the average citizen to understand how unimportant handguns are to Big Army. Below boots, MREs, and sleeping bags in terms of winning ground wars. GEN Milley's original point was that the Army had already wasted too much time and money on a very irrelevant piece of gear, and should just go with the simplest decent solution: the Glock 19, which was already in procurement channels for some USSOCCOM elements.
I have no inside baseball, just a hunch with how it all played out.
Jon