I think it's def a cultural thing on why they're hard on drugs outside of tobacco. Also, I think we have to look at their governments are usually super conservative and they're on islands, so they can control the flow of drugs that enter their countries. It's interesting that because it's harder to get stuff like weed there that they resort to meth.
I think if you were to look historically they're probably harsh on drugs due to the opium that happened in China. Also, I think there have been some wars in the past that impact drug usage and laws. It's crazy though because their attitude towards weed for example that it's as bad as crack.
Anyway, if I were to take a wild guess it mostly boils down to culture values, conservative governments, and results of wars. I doubt they change their stance about it because even when an Asian person visits a western country they get shook if they hear about weed. It's just sad how hard on it because the media and fans will hound a person to a deep depression because of it. Also, they have to resort to heavy drinking for an escape which can be more damaging than weed and other drugs imo