You obviously failed to read the Royal Chronicles of Cambodia. Khmer culture nearly went extinct during the reign of Ang Mey, when the Vietnamese occupation took place. Vietnamese culture and customs were imposed onto the local populace. Khmer culture was revitalized during the reign of Preah Bat Norodom by the Siamese court. During the fall of Yasodharapura in 1432, the residents of Angkor were resettled in Ayutthaya. If you no longer have something, it is no longer your's. Khmer culture had to be reintroduced by the Siamese because the Vietnamese nearly succeeded in wiping out and assimilating the Khmer people. If it weren't for Siamese intervention in the 1800's, Cambodia's fate would be the same as Champa's.