The Fukushima plant had emergency generators, but they ran out of fuel when the tsunami washed the tanks away. The Japanese authorities were unable to run a powerline to the plant before the THIRD level safety systems (battery backup) ran out of juice.
There is no such thing as an absolute fail-safe system. What if the NG pipeline is breached by the same event? What if the propane tank fails at the same time as the event?
The diminishing returns on safety investments obviously precluded adding the standby system. Reality is that hard choices must be made, and sometimes hindsight puts the lie to earlier decisions.
The state has had only 44 years to correct the problem.
Gotta give them more time.