Considering this was the biggest storm surge the east coast has seen in almost 90 years that would be the reason, no?
It's not like they put backup generators on stilts (Maybe they should though in hurricane/tsunami prone areas. After all, even the backup generators for the Fukushima Nuclear reactors cooling systems even got flooded out the same way).
Generators don't work underwater, and 15 feet covers 1st floor and trailer mounted. Electrical equipment doesn't work submerged in water, unless it's meant to of course.
The Long Beach Central Office got zero to six inches of water on parts of its first floor. Most of the place didn't get any. The place is up two steps and the street got less than a foot at that location. Certainly the trailer generator didn't get any water. I know every employee left the CO during the storm, which is quite unusual. Typical of morale issues these days. Does anyone have any real information, other than incorrect guesses about the water height?