Uhh... so

Hikikomori:s likely have some mental illness, based on what I read about the issue. The onset time matches (late adolescence/early adulthood) and several mental illnesses result in "severe social withdrawal". Also the percentage of populatuion matches...

It's not ausitm though (that has a much earlier onset).

So whatever... Someone tell them. Maybe a few of them would prefer to get help and become "normal citizens" again. It's possible.