Continuity mistake: While the close-ups showed heavy ice build-up on the doomed plane, the long shots showed no ice at all.
Visible crew/equipment: When the search aircraft make their last fly-by over the Duke and his crew who are supposedly stranded on a frozen lake, parallel vehicle tracks are plainly visible, leading to their aircraft, and around it.
Revealing mistake: When ice is shedding from the plane's wings, the chunks slowly slide forward and then down the leading edge. Loose chunks should have flown off rapidly to the rear due to the airflow.
Revealing mistake: During the first aerial search scene, at a point which is supposed to be deep into uncharted territory, a snow-covered road can be prominently seen skirting the shore of a big lake.
Factual error: All of the flight scenes show the AC with the USAF star and stripes logo and the fuselage said "United States Air Force" quite prominently. The Air Force was not created as a separate service until 9/18/1947. Prior to that, the Air Force was part of the Army and known as the US Army Air Corp or US Army Air Force (USAAF). The movie was released 9/3/1953, based on a book written 1944, based on a true story of a flight February 3, 1943 and the Air Transport Command. The ATC was a designation from 1942-1948 only and when the AF was established in late 1947, it was not part of the service. There could not have been a C-47 with "United States Air Force" designation when the book was written, when the real event occurred or when it was portrayed.
Answer: Because after eating it as part of their rations throughout WWII many ex GIs never swore to touch the stuff.