Indeed.
I don't buy, "they didn't have cars."
I'll bet the ranch, anytime they wanted to go & visit Aunt Mabel in FL, or wherever, they knew how to get on a bus, at a moment's notice.
The buses weren't running. Most of them have probably not left the city of New Orleans in their lives. These are not a traveling people.
I agree they did not do all they could to save themselves. But many had little knowledge of the ways of the world outside their neighborhood.