I'm not a Japanese but I would say that the social expectations are too high: at X age you should be working for a company, at Y you should be married, at Z age

I'm not a Japanese but I would say that the social expectations are too high: at X age you should be working for a company, at Y you should be married, at Z age you should own a house... some people can't handle that pressure, specially if something has gone wrong. There's a webcomic called Re:Life in which this is shown.