Conversation so far:
What was the Cultural background for the Departures (2008) film?
Japanese funerals are highly ritualized affairs which are generally--though not always--conducted in accordance with Buddhist rites.
How do the Japanese funerals go against the grains of Buddhist rites?
CANNOTANSWER.
What else can you tell me about the cultural background for the film?
Despite the importance of death rituals, in traditional Japanese culture the subject is considered unclean as everything related to death is thought to be a source of kegare (defilement).
What was the greatest cultural background factor affecting the film?
People who work closely with the dead, such as morticians, are thus considered unclean, and during the feudal era those whose work was related to death became burakumin (untouchables).
Did this promote controversy?
CANNOTANSWER.
What else in the background really stands out?
Until 1972, most deaths were dealt with by families, funeral homes, or nokanshi.

Question: What caused the change?
Self-contained rewrite: What caused the change in how families dealt with death in 1972 in Japan?