I don't know, which is why I asked the question.
We have had incidents far more frequently than "every ten or twelve years" where a FEMA capability could have been useful.
Just off the top of my head...Katrina, recent flooding around Baton Rouge, Harvey in Texas, and now Irma in Florida. These are just the ones directly affecting my immediate family.
Here is a list just of hurricanes:
https://www.mapsofworld.com/hurricane/dates.html
Certainly use of Naval vessels is a good thing, but a vessel specifically equipped for the purpose might prove useful.
And just what could a carrier have done that couldn't have been done by land? I suspect the carrier will sail around a bit, maybe fly some supplies to the keys. But 99% of the disaster recovery resources will come down I-95 and I-75. Just like they came down I-45 and I-10 for Harvey.
But two your point, the Navy ships in question are all well over 30 years old, some are pushing 60. Navy ships are expensive to run, labor intensive, and at a point where spare parts are impossible to get. Keeping an old Navy ship around on the off chance you will need to use it is a pretty high-cost solution in search of a need.