It's the same reason why fictional commandos like Rambo and buddies have less kills and not so daring achievements as some historically documented cases.
Fiction writers try to push the limits of what readers will [try to] believe, while reality simply ignores those limits.
>He served in the Boer War, First World War, and Second World War; was shot in the face, head, stomach, ankle, leg, hip, and ear; survived two plane crashes; tunnelled out of a POW camp; and bit off his own fingers when a doctor refused to amputate them. Describing his experiences in World War I, he wrote, "Frankly I had enjoyed the war."
Veteran of the French and Indian wars. At the age of 78 he participated in the Battle of Lexington and Concorde, where he was bayoneted, beaten and shot in the face. He recovered and died of old age at 96.
After escaping a German concentration camp and walking 93 miles to Italy he was redeployed to Burma, but Japan surrendered before he could make it to India: "If it wasn't for those damn Yanks, we could have kept the war going another 10 years."
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In later years, Churchill served as an instructor at the land-air warfare school in Australia, where he became a passionate devotee of the surfboard. Back in England, he was the first man to ride the River Severn's five-foot tidal bore and designed his own board.
Seems like the only reason no one has made a movie about him is because no one would believe it.
http://en.wikipedia.org/wiki/Jacob_C._Vouza Native of Guadalcanal, tied to a tree, tortured, stabbed, and left for dead by the Japanese when he was found with a small American flag in his loincloth. Chewed his way through the ropes and staggered several miles to the Marines to warn them of the Japanese battalion he encountered before being hospitalized. Later served as a scout for Carlson's Raiders.
Speaking of which...
http://en.m.wikipedia.org/wiki/Evans_Carlson Marine officer who went to China and lived alongside Mao Zedong and studied guerrilla warfare. Later formed and led a special Marine unit that was organized as a Maoist guerrilla unit.
Well, to be fair, Rambo was tasked with taking photographs and not engaging the enemy at a time when there was supposedly no active military action against Vietnam.
Fiction writers try to push the limits of what readers will [try to] believe, while reality simply ignores those limits.