Japans Regierung weist 42 Unternehmen an, Pläne zur Verhinderung arbeitsbedingter Todesfälle und schwerwiegender Probleme zu erstellen

I think the main cause is the harassment at work forcing employees to overwork. Japan has a major problem with harassment at work. Foreigners often voice harassment at work but it seems like many Japanese are keeping it in to themselves and end up committing suicide.