Redundancy is something you'd consider for some businesses in areas where outages are somewhat common.
The investment needed for a backup power in this case is probably not worth the times it will be used. You'd need a second power plant running 24/7 along with the main grid, just for an event that may happen once every 10-20 years (according to what
@TheLostSwede indicated), and the upkeep of said backup would go directly to the consumer.
These guys probably did the math and the result was: not worth it.