Life is hard. It is tempting to take something to ease the pain, even if temporary, even if you know it will hurt more than help in the long run. And then there is the risk of becoming addicted, as with all drugs including alcohol. Instead of turning to drugs, East Asian countries have traditionally been able to find solace in their religious and spiritual practices that encourage social harmony, despite all of its negative aspects.Culturally, marijuana is about the last drug that the Japanese government would want to encourage.
It goes completely against the gambaru mentality that is instilled into the Japanese population. The prospect of making available a drug that encourages physical inertia and removes people's everyday filters, making them completely content to examine the grain on a piece of wood for hours on end as if seeing it for the first time, would fill the average lawmaker or boss with horror. I mean, what the hell is the point of a person if they are not working or consuming?
Drugs like marijuana will ‘work’ in any society if the numbers of users who are rendered net non-contributors of society are vastly outnumbered by the workers and consumers who can support a social and economic welfare system to compensate. Not sure Japan has the tolerance for that level of social disorder that is found in the US.