These are called NEET (not in education, employment, or training) in the west with a similarly large populace. I don't think we can attribute this to just Japan. Canada also has a NEET population problem.
I would rather attribute this to the rigors of society which doesn't allow for different development paths. Adulthood is a hard transition and some people need more time or different structures than others, but society doesn't allow for that. In the past these people would be vagrants until they "settled down" and could somewhat easily re-integrate back to society (employment as a stablehand could go to ferrier, horse trainer, or other land management). Now, with the need for specialization and training paired with age expectations, there's much less room.
It's only reasonable to decide your window is missed and therefore there's nothing for you.
I would rather attribute this to the rigors of society which doesn't allow for different development paths. Adulthood is a hard transition and some people need more time or different structures than others, but society doesn't allow for that. In the past these people would be vagrants until they "settled down" and could somewhat easily re-integrate back to society (employment as a stablehand could go to ferrier, horse trainer, or other land management). Now, with the need for specialization and training paired with age expectations, there's much less room.
It's only reasonable to decide your window is missed and therefore there's nothing for you.