I was a teacher at an English Conversation School, more than 30 years ago, and I think that there is more to them -- or at least there was.

Where I lived, this was one of the few places to interact with a foreigner and practice English (often before going on an overseas holiday or work contract). Even better, it was a safe and controlled environment.

One of the crucial hurdles for Japanese people learning English has always been a lack of confidence and fear of looking foolish in public.

It didn't do much for English ability, because how could it when the class is only one hour a week?

Many of the schools were get-rich-quick schemes, as you say, but that doesn't mean they didn't provide a valuable function, even if they didn't contribute directly to English ability.