Anecdotally from friends, I'd say the top three reasons are:
* Lack of money
* Lack of time off from work
* Lack of English skills, making travel abroad intimidating. In previous generations this was counteracted by bus tours with Japanese guides, but those are seen as lame by the younger generations.
* Lack of money
* Lack of time off from work
* Lack of English skills, making travel abroad intimidating. In previous generations this was counteracted by bus tours with Japanese guides, but those are seen as lame by the younger generations.