My theory is that the American government has become so fashy since the 40s that it’s effectively impossible for a truly radical leftist movement to exist. The FBI/CIA/NSA all spy and infiltrate any leftist org to destroy them from within while the police, capitalist media propaganda and politicians destroy them from the outside.
The only way out is another country. (And not idiotic smug spite voting trump to “teach the Democratic Party a lesson”)
I really hate the "they have a single culture" theory of why Japan has different problems. I think the difference is that the relationship between the state and citizens is totally different.