Why the ninjas in kung fu films were nearly always the bad guys
Japanese ninjas became a global cultural phenomenon in the 1980s, but they turn up relatively infrequently in Hong Kong martial arts films. When they do appear in movies such as the Shaw Brothers classics Heroes of the East (directed by Lau Kar-leung) and Five Elements Ninjas (by Chang Cheh), they are portrayed as cheats who have no respect for honour...
Source: asiaone.com