I get that this comment is hyperbole, but it's not entirely true. The trauma experienced by U.S. military personnel, and processed through movies, is primarily moral injury, knowing that they went to war and did terrible things unjustly, unnecessarily, based on lies. (Contrast this with the trauma experienced by the protagonists in The Best Years of Our LIves, veterans of what is seen as a just, necessary war. They struggle with life after war, not guilt about what they did in it.) There are movies from other countries which process the same sort of trauma, such as the Israeli film Waltz with Bashir, made by a former IDF soldier processing his role in the 1982 Lebanon War.
Point is, 'merica doesn't have mentally-weak, or entitled, soldiers compared to other nations, it just gets into a lot of morally-indefensible wars. (And Israel causes moral injury to many of its people with its morally-indefensible wars, too.)