The reason is unlike in World War II (and Vietnam) there is no actual shared sacrifice amongst the American people. WWII was a shared burden across the entire American populace. There is no shared sacrifice and no shared burden during the last 8 years.
418500 Americans lost their lives in WWII and millions more were injured. Additionally, the American People aided in the War effort, scrimped and saved, worked with the Department of War and in the Armed Forces and knew large swaths of the American populace also sacrificed and suffered.
While, today a vast majority of Americans do not have even a tangential connection to either theater of Operations. This is why no one cares about War deaths, or TBI and homeless Veterans.
And those making movies are even further removed. No modern "star" today would even consider dropping a Hollywood career for service. There aren't a Vic Mature or Wayne Morris amongst today's stars. No today's Hollywood elite mimic World War II Chicken Hawks Ronald Reagan and John Wayne and pretend to be in the military...
Then, when the war ended most Americans had a real connection to it and knew something about war and the military. They knew how to portray the war and soldiers. Today's Americans and Hollywooders don't and it shows.
Update:
I left an updated comment over at Nixon's. It's a line, from the documentary Gunner Palace, which sums up the American publics' (shopping not withstanding) view of Iraq:
"Someone being sympathetic to this? I don't know if I'd be sympathetic if I wasn't in the Army. After you watch this, you're gonna go get your popcorn out of the microwave and talk about what I said, and you'll forget me by the end of this.” ~SGT Beatty, Gunner Palace.
