Isn't that strange ? I mean cable should be more easily broken than airwaves, no ? Is it because the landlines in Japan are designed to resist and the cell phone tower got power disruption ?
Also, it is much cheaper to provide enough cable than radio transceivers. Thus mobile networks nearly always run close to full capacity... ever had "network busy" on your phone when dialing in a downtown? So they are easily overwhelmed in emergencies. With landline, in contrast, you always have the line, so it is mostly a matter of installing big enough BX station.