Aside from the sick, infirm, etc., were the emergency responders who were told to wait AT HOME for the calls. This includes police, fire, and medical personnel as well as support staff. Another group who didn't evacuate were the students at the universities who didn't have cars--and couldn't rent because they were too young. Amazingly, the universities told them they would get them out, then at the last minute said they couldn't--no explanation why.
There is, however, one group I have no sympathy for. I know in my heart of hearts that the ones we saw looting stayed behind precisely for that purpose. To loot. I have NO doubt that as soon as people started to leave, they were breaking into houses as quickly as possible before the storm hit. I only wish more of them had "washed away."
Tulane said it would have bus service to take the remaining Tulane folks out at noon on Sunday. Did they not arrive?