“ So it was not without irony that, on Jan. 19, 2017, the Army announced that its new sidearm would be a SIG Sauer”
Not ironic at all. The Sig 226 is much pricier and not modular like the 320. It is also heavier. It would be ironic if they had chosen the 226 perhaps but this was a new acquisition decades apart with very different handguns submitted for trials.
As far as the Remington R9, my guess is it was absolutely intentional to not submit it. Remington has had some major QC issues as of the last 10 years and their R51 was so bad they recalled them all and stopped selling it for years while they supposedly worked the bugs out. If/when the R9 failed miserably there would be even more fallout from the consumer market and that might just be the final nail in the PR coffin for the once great company.