What motivated the US Army to buy 8,000 1911-A1 .45 ACP's?
I'm not sure what you're talking about here.
The Army (or any other branch of the military) isn't buying these pistols. They've been government/military property ever since they were manufactured. They aren't all "Army" pistols, either, and never were. Every branch of the military used the 1911A1 during the WWII, Korea, and even on into Vietnam. The military (through Congress) is transferring the pistols to the CMP to sell to people like us. Civilians.
These 1911s/1911A1s are probably at least 70-years-old, maybe older. They're WWII era pistols made by Colt, Ithaca, and Remington Rand. Maybe there'll be some US&S and Remington UMC pistols in this lot, who knows? Maybe there'll be some genuine collectors' pistols in the lot. There's simply no way to tell at this stage of the process. Anticipation is part of the fun...what'll be in the big Grab Bag? Who'll get a real prize?
8,000 pistols is a drop in the bucket compared to the numbers of pistols made for the war effort. According to Clawson, by the end of the war, Remington Rand had produced over 875,000, Colt had made over 628,000, and Ithaca manufactured 335,467 pistols.
I look for a lot of these pistols to be arsenal reworks, and marked as such, especially the Remington Rands and Ithacas. Some of them will have been reworked/repaired by the CMP. They won't be allowed to sell any non-functioning pistols. I think "originality" will be iffy at best, maybe impossible to prove in a lot of cases.
This process seems to be moving a lot faster than a lot of us thought it would. We might see the pistols selling by Fall, or at least by the end of the year.