It is my understanding that they have had trial runs wwith evacuation in NOLA. However, in this real situation, not deploying the buses was an ecomonic decision to save the buses. This resulted in death of many people. Someone made this decision, and someone will be held accountable.
My understanding of what happens is when a city declares a mandatory evacuation, the city is responsible for removing the infirm and those without transportation.
Somebody stepped in it up to their neck by not using the buses!