Reading the book, so many of them froze to death. They overran foxholes that had Communists in them whose ears, bare hands, and bare feet were literally encased in ice.
I can’t hit the broadside of a bull’s ass with a handful of peas with an iron site past 100 yards, I can’t imagine what it would be like with frozen fingers and muscles shivering uncontrollably trying to sight in.
OTOH, our guys were cold and frozen too, and seemed to shoot reasonably well, but...the Marines were Marines, and they fared better than those unfortunate Army chaps.
The ad hoc teams put together from Marines by taking cooks, mechanics, and anyone else were still Marines, but those poor 8th Army guys were in many cases guys who hadn’t shot a weapon since boot camp, and even then just barely so.
That old USMC adage “Every Marine a Rifleman” was true back then. But for those Army guys taken from kitchens and such had no such training, and they got slaughtered by the overwhelming numbers.