Seriously, if you're a celeb over there and caught smoking a joint, your career is basically over.
Even the infamously prudish U.S. is more accepting of it.
I'm guessing it's a leftover of U.S, imperialism, like how all their porn is still censored.
You can look up an ukiyo-e painting of a woman fucking an octopus. It's not just a modern phenomenon.
Don't forget that "The Dream of the Fisherman's Wife," i.e. a woman getting eaten out by an octopus, was designed by Hokusai, whose "Great Wave" is probably the most well-knoen ukiyo-e print. It's generally argued that nearly all the famous ukiyo-e artists also did shunga (erotic pictures), and that something like 3/4 of all ukiyo-e prints in circulation were shunga.
At the same time, it was technically illegal to be making these things in the first place, since they had to be distributed without an official stamp from the government censor. So in Japan freaky shit and government censorship working hand in hand goes all the way back to the beginnings of modernity itself.